JPH1090623A - Laser beam optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam optical scanner with high detection capability of out-of-focus capable of focus adjusting in a very short time. SOLUTION: In the laser beam optical scanner mainly constituted of a laser diode 1, a focusing lens 3, a polygon mirror 6 and an fθlens 7 and printing an image on a photoreceptor drum 30, a beam detector 100 is set up in the vicinity of a position optically nearly equivalent to the surface of the photoreceptor drum 30. This detector 100 is constituted of a first filter 101 having a space grating parallel to the laser beam scanning direction b, a second filter 102 having the space grating tilting by a minute angle for the laser beam scanning direction b, cylindrical lenses 103, 104 constituting a minute optical system and a photoelectric conversion element 105 light receiving a laser beam transmitting through the filters 101, 102.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam scanning optical device, and more particularly to a laser beam scanning optical device incorporated as an image printing means in a laser printer or a digital copying machine.

[0002]

2. Description of the Related Art In recent years, laser beam scanning optical devices incorporated as image printing means in laser printers and digital copying machines have been capable of printing at high density in order to improve image quality. For this reason, the spot diameter of the laser beam on the surface to be scanned (photoreceptor) becomes smaller, and the allowable depth of focus becomes smaller. Then, when the optical device generates heat during use and the optical element and its holder undergo thermal expansion due to environmental changes, particularly, the light-condensing position shifts in the front-rear direction of the surface to be scanned, and the shift maintains high image quality. And it has become unacceptable.

In order to cope with such a problem, an apparatus described in Japanese Patent Application Laid-Open No. 2-51119 detects a focused state of a laser beam with a detecting element having a single grating filter and optimizes a lens. Moved to the position. In the apparatus described in Japanese Patent Application Laid-Open No. 4-155304, a laser beam focusing state is detected by a detector constituted by a knife edge disposed before and after a surface to be scanned and a photoelectric conversion element, and a lens is optimized. Moved to the position.

[0004]

In the former (Japanese Patent Laid-Open No. 2-51119), since a single grating filter is used, it is possible to determine whether the condensing position is in the front focus state or the rear focus state. In addition, it is necessary to move the lens forward or backward to perform the focus adjustment, so that quick adjustment cannot be performed. In particular, it is difficult to adjust the focus in a short time (several hundred milliseconds) between printed pages, and there is an inconvenience that the focus is slightly shifted during continuous page printing.

In the latter case (Japanese Patent Application Laid-Open No. 4-155304), since the knife edge is used, it is possible to determine whether the shift of the focusing position is before or after, but the detection waveform of the laser beam is single-shot. The detection value is unstable. For this reason, there is a disadvantage that the detection capability is low. SUMMARY OF THE INVENTION It is an object of the present invention to provide a laser beam scanning optical device having a high defocus detection capability and capable of performing focus adjustment in an extremely short time.

[0006]

In order to achieve the above object, a laser beam scanning optical apparatus according to the present invention is disposed near an optically equivalent position to a surface to be scanned, and is radiated from the laser light source. And a light receiving element for receiving the moire fringe pattern generated by the moiré fringe generation means. For example, the moiré fringe generating means includes, in order from the laser light source side, a first filter having a striped spatial grid, and a striped space inclined at a small angle with respect to the direction of the spatial grid of the first filter. And a second filter having a grating.

The striped spatial grating of the first filter may be parallel to the main scanning direction of the laser beam, or may be parallel to the sub-scanning direction. The light receiving element preferably has a plurality of light receiving surfaces, for example, a multi-division photodiode, a plurality of photodiodes, a combination of a plurality of line sensors, an area CCD, a four-division sensor, or the like is employed. Is done.

In the above configuration, the laser beam emitted from the laser light source forms moire fringes on the light receiving surface of the light receiving element via the moire fringe generating means. When the focus position of the laser beam shifts before or after on the light receiving surface, the shape of the moire fringes, more specifically, the inclination of the moire fringes changes. The change in the inclination of the moire fringes is reversed when the focus position of the laser beam is shifted in front of the light receiving surface and when it is shifted after. Therefore, by detecting the change in the inclination of the moiré fringes with the light receiving element, it is possible to measure the shift amount of the light condensing position and determine whether the shift of the light condensing position is ahead or behind the light receiving surface.
Therefore, the focus adjustment is completed by driving the adjusting means for adjusting the beam focusing position in either the front or rear direction.

Further, in the laser beam scanning optical device according to the present invention, a reduction optical system is provided between the moire fringe generating means and the light receiving element. Here, the reduction optical system may be, for example, a combination of two cylindrical lenses or a combination of two.
It is composed of two positive lenses. With the above configuration, the reduced moire fringes are projected on the light receiving surface.

The laser beam scanning optical device according to the present invention is a photoelectric conversion device, wherein the light receiving element has a plurality of light receiving surfaces and outputs an electric signal corresponding to the laser beam incident on each of the light receiving surfaces. And a phase difference detecting means for detecting a phase difference of each electric signal output from the photoelectric conversion element. With the above configuration, a change in the inclination of the moire fringes is detected based on the phase difference between the waveforms of the output signals from the plurality of light receiving surfaces, and the beam condensing position is determined.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a laser beam scanning optical device according to the present invention will be described below with reference to the accompanying drawings.

[First Embodiment, FIGS. 1 to 39] (Overall Configuration of Laser Beam Scanning Optical Device) In FIG.
, A collimator lens 2 and a focusing lens 3
, A cylindrical lens 4, a plane mirror 5, a polygon mirror 6, and an fθ lens 7 (lenses 7a, 7b, 7c).
), A plane mirror 8, an SOS cylindrical lens 16, an SOS optical sensor 17, and a beam detector 100.

The laser diode 1 is modulated (ON / OFF) based on print data input to a drive circuit (not shown).
It is controlled and emits a laser beam when turned on. This laser beam is converged substantially parallel by the collimator lens 2, the focusing position is adjusted by the focusing lens 3 (described in detail below), and reaches the polygon mirror 6 from the cylindrical lens 4 via the plane mirror 5.

The polygon mirror 6 is driven to rotate at a constant speed about an axis of rotation 6a in the direction of arrow a. The laser beam is deflected at a constant angular velocity on each deflecting surface based on the rotation of the polygon mirror 6 and enters the fθ lens 7. The laser beam transmitted through the fθ lens 7 is reflected by the plane mirror 8 and then condensed on the photosensitive drum 30,
The upper part is scanned in the direction of arrow b. lens 7 mainly has a function of correcting the laser beam deflected by the polygon mirror 6 at a constant angular velocity to a constant main scanning speed on the surface to be scanned (photosensitive drum 30), that is, a function of correcting distortion. Have.

The photosensitive drum 30 is rotated at a constant speed in the direction of arrow c, and an image (electrostatic charge) is formed on the drum 30 by the main scanning in the direction of arrow b by the polygon mirror 6 and the sub-scanning of the drum 30 in the direction of arrow c. Latent image) is formed. Also,
The laser beam at the leading end in the main scanning direction of the laser beam is reflected by the mirror 15 and the SOS cylindrical lens 16
And enters the SOS optical sensor 17. The beam detection signal output from the SOS optical sensor 17 generates a vertical synchronization signal for determining a printing start position for each scanning line.

The focusing lens 3 is mounted on a base plate 20, and an output pinion 22 of a stepping motor 21 is mounted on a rack 20 a formed on a side surface of the base plate 20.
Are engaged. By rotating the stepping motor 21 forward or backward by the signal processing circuit 24, the control circuit 25, and the focusing lens drive control unit 26,
The lens 3 is movable in the front-rear direction on the optical axis, and by this movement, the focusing position of the laser beam on the photosensitive drum 30 is adjusted.

(Explanation of Beam Detector) Beam Detector 10
Numeral 0 is installed outside the image area near the optically substantially equivalent position with respect to the surface to be scanned, and detects the focusing state of the laser beam on the surface to be scanned. More specifically, as shown in FIGS. 1 and 2, grating filters 101 and 102, cylindrical lenses 103 and 104, and a photoelectric conversion element 105 arranged in the optical axis direction.
It is composed of The grating filters 101 and 102 have striped spatial gratings A and B, respectively. The spatial grating A is parallel to the main scanning direction b of the laser beam L, and the spatial grating B is inclined by a small angle.

Here, it is assumed that the spatial grid A of the grid filter 101 is arranged in a direction perpendicular to the main scanning direction b, that is, parallel to the sub-scanning direction, as shown in FIG. When the laser beam L is scanned, the laser beam L is sequentially blocked by the spatial grating A, and the light receiving surface 105 is scanned by one scan.
The light quantity of the laser beam L incident on a and 105b decreases. For this reason, the contrast of the moiré fringes is reduced, and a problem occurs in that the photoelectric conversion element 105 cannot detect the moiré fringes. Further, as shown in FIG. 4, when the laser beam is sequentially scanned in the order of L ₁ , L ₂ and L ₃ (the lattice filter 102 and the cylindrical lens 10).
3, 104 are omitted), the moire fringes slightly shift in the main scanning direction b in accordance with the shift of the laser beam, the laser beam L ₁ irradiates the portion R ₁ of the photoelectric conversion element 105, and the laser beam L _{2 2} and the laser beam L ₃ is R ₃
Is irradiated. Therefore, for example, the point p is irradiated with the laser beam L _1, not irradiated with the laser beam L ₂ , and irradiated with the laser beam L ₃ . Since this phenomenon occurs within a very short time, it becomes difficult to specify the shape of the moire fringes, and the moire fringes cannot be detected.

On the other hand, in the first embodiment, as shown in FIG.
Since the spatial grid A of the grid filter 101 is arranged parallel to the main scanning direction b, a constant amount of light always enters, and the moiré fringes 35 can be detected with high accuracy. The photoelectric conversion element 105 is a two-division photodiode having upper and lower light receiving surfaces 105a and 105b for receiving a laser beam, and each of the light receiving surfaces 105a and 105b outputs a current proportional to the amount of received light.

(Explanation of Moire Fringes) By the way, moire fringes 3
5 can be represented by the following linear equation (1). Here, x is the coordinate in the main scanning direction b, y is the coordinate in the sub-scanning direction, α is the small inclination angle of the spatial grid B, and f is the light receiving surface 1
The pitch size of the spatial grating A projected on the light receiving surfaces 105a and 105b, and g is the pitch size of the spatial grating B projected on the light receiving surfaces 105a and 105b.

[0021]

(Equation 1)

In the linear equation (1), the coefficient ｛cosα−
(G / f)｝ / sin α means the inclination of the moire fringes 35. This coefficient is derived as follows. As shown in FIG. 5, xy coordinates having the origin at the intersection of the spatial gratings A and B projected on the light receiving surfaces 105a and 105b and the moiré fringe are set. Next, a linear expression for displaying the line image 41 of the spatial grid B is obtained.

Assuming that the y coordinate of the intersection of the line image 41 and the y axis is h, g = hsin ((π / 2) −α).
Since hcosα, h = g / cosα. Since the inclination of the line image 41 is tan α from FIG.
Is expressed by the following linear equation (2). y = (tan α) × x + (g / cos α) (2) Next, when the x coordinate of the intersection of the expression y = f representing the line image 42 of the spatial grid A and the linear expression (2) is obtained, f = (tan α) × x + (g / cos α) x = {f− (g / cos α)} / tan α Therefore, a straight line 43 indicating the center of the moiré fringe 35 is expressed by the following linear expression (3). Is done.

[0024]

(Equation 2)

Therefore, the inclination of the moire fringes 35 is Δcos α
− (G / f)｝ / sin α. By the way, if the pitch dimensions of the spatial gratings A and B are d ₁ and d ₂ , and the distances from the focus position to the spatial gratings A and B are l ₁ and l ₂ , the following relational expression (4) is obtained. . f / g = (l ₂ d ₁ ) / (l ₁ d ₂ ) (4) From the equations (1) and (2), the inclination of the moiré fringes 35 is

[0026]

(Equation 3)

## EQU1 ## The pitch dimension of the moire fringes 35 is P, and the angle formed by the moire fringes 35 with respect to the sub-scanning direction is φ.
Then, the following relational expression (6) is obtained. P = (f / sin α) × cos (φ−α) (6) As shown in FIG. 6, when the focus position Z1 shifts by Δ1 to Z2, the front focus state is established, and the moire fringe at that time is obtained. The slope of 35 is

[0028]

(Equation 4)

## EQU1 ## The inclination of the moire fringes 35 in the back focus state is as follows.

[0030]

(Equation 5)

## EQU1 ## (7) and (8) show that the beam detector 100 is focused on the laser beam L (optically equivalent position).
This is the inclination of the moire fringes 35 when the moiré fringes 35 are arranged further rearward. When the beam detector 100 is arranged ahead of the focus position of the laser beam L, the signs before and after Δl are reversed in (7) and (8). (5), (7), and (8) show that the inclination of the moiré fringes 35 changes due to defocus. That is, the bright portion of the moiré fringe 35 in the focused state is orthogonal to the main scanning direction b (see FIG. 12), and the moiré fringe 35 in the front focus state rotates clockwise and tilts to the right (see FIG. 13). The moiré fringe 35 in the rear focus state is rotated left and inclined to the left (see FIG. 14).

(Spot Diameter of Laser Beam) Here, the spot diameter of the laser beam for accurately detecting the change in the inclination of the moiré fringes 35 was examined. As shown in FIG. 7, in the main scanning direction (direction of the space lattice A), the spot diameter D _L of the laser beam L on the grid filter 101 is set to be smaller than the interval Q of the Moire fringes 35, the spot Lb When located between two moire fringes 35 ((a)
And (c)), the portion where the spot Lb and the moire fringe 35 overlap has a small area. Therefore, the amount of light received by the photoelectric conversion element 105 increases, and the output current increases. on the other hand,
When the spot Lb is located at the center of the moiré fringe 35 (see (b)), a portion where the spot Lb and the moiré fringe 35 overlap has a large area. Therefore, the amount of light received by the photoelectric conversion element 105 decreases, and the output current decreases.

FIG. 8 shows the light receiving surface 105a (or 105
It is the graph which displayed the output waveform which converted the output current of b) into the voltage. 8, the points (a) and (c) are outputs when the spot Lb is located between the two moire fringes 35, and the outputs when the point (b) is located at the center of the moire fringe 35. is there. Conversely, as shown in FIG. 9, the spot diameter D _L of the laser beam L on the grating filter 101
Is set to be larger than the interval Q between the moiré fringes 35, when the spot Lb is located between the two moiré fringes 35 (see (a) and (c)), the portion where the spot Lb and the moiré fringe 35 overlap is formed. Is wider, but the photoelectric conversion element 10
5 does not become so small. On the other hand, when the spot Lb is located at the center of the moiré fringes 35 (see (b)), the portion where the spot Lb and the moiré fringes 35 do not overlap is wider, but the amount of light received by the photoelectric conversion element 105 is not so large.

FIG. 10 shows the light receiving surface 105a (or 10
It is the graph which displayed the output waveform which converted the output current of 5b) into the voltage. In FIG. 10, points (a) and (c) are outputs when the spot Lb is located between the two moiré fringes 35, and outputs when the point (b) is located at the center of the moiré fringes 35. is there. Comparing the graphs of FIG. 8 and FIG. 10, it is found that the moiré fringes 35 in the main scanning direction (the direction of the spatial grating A)
It can be seen that when the interval Q is set to be larger than the spot diameter D _L of the laser beam L on the grating filter 101, the contrast of the output waveform is better, and the change in the inclination of the moiré fringes 35 can be detected with higher accuracy.

Further description will be made using specific numerical values. In FIG. 5, the pitch dimension P of the moiré fringes 35 is obtained by the relational expression (6).
The direction Q of the moiré fringes 35 is as follows: Q = P / cosφ = (f / cosφ · sinα) × cos (φ−α) Therefore, the interval Q of the Moire fringes 35 to be larger than the spot diameter D _L of the laser beam L on the grid filter 101, it is sufficient to satisfy the following equation (9).

D _L <(f / cos φ · sin α) × cos (φ−α) (9) From the above results, the spot diameter D _L in the main scanning direction on the grating filter 101 is _expressed by the relational expression (9). If it is set to satisfy, the contrast of the output waveform is improved, and the moire fringe 3
5 can be accurately detected. (About the pitch error of the spatial grid)
In the case of, the inclination changes due to the pitch error of the spatial gratings A and B of the grating filters 101 and 102 in addition to the case where the focusing state of the laser beam changes. That is, the moire fringes 35 due to the pitch errors Δd ₁ and Δd ₂ of the spatial gratings A and B.
The effect of the pitch error Δd ₁ of the spatial grid A was small, but it was found that a large pitch error Δd ₂ of the spatial grid B had a large effect on the tilt change of the moire fringes 35 even when the pitch error Δd ₁ of the spatial grid A was small. Was. From this experimental result, in order to stably detect the defocus, it is necessary that the pitch error Δd ₂ of the spatial grating B satisfies the following relational expression (10). Here, Δl ₁ is the deviation of the interval from the beam focusing position to the grating filter 101, and Δl ₂ is the deviation of the interval from the beam focusing position to the grating filter 102.

D ₂ − {(l ₂ −Δl ₂ ) / (l ₁ −Δl ₁ )} · d ₁ <Δd ₂ (10) The relational expression (10) shows the focus position with respect to the change in the inclination of the moire fringes 35. Contribution due to deviation Δl and pitch error Δ of spatial grid B
It is an equation derived from the result of comparing the contribution by d ₂ . If the pitch error Δd ₂ satisfies the relational expression (10), the change in the inclination of the moiré fringes 35 due to the focus position deviation Δl becomes larger than the change in the inclination of the moiré fringes 35 due to the pitch error Δd ₂ , and the defocus is accurately performed. It can be detected well.

The relational expression (11) indicates that the photoelectric conversion element 1
This is a condition for forming a detectable moiré fringe 35 on the light receiving surfaces 105a and 105b of FIG. Δd ₂ <d ₂ − (l ₂ / l ₁ ) · d ₁ (11) If the pitch error Δd ₂ satisfies the relational expression (11), the inclination change of the moire fringes 35 due to the pitch error Δd ₂ is large. There is no fear that the defocus will not be detected due to too much of a focus, and the defocus can be detected stably.

A detailed description will be given using numerical values.
The pitch d ₁ of the spatial grating A is 125 μm, and the spatial grating B is
40mm distance l ₁ of the pitch dimension d ₂ 250 [mu] m, from the in-focus position to the spatial grid A of the space lattice B from the in-focus position
When the distance l ₂ to the head is set to 80 mm, the pitch error Δd ₂ of the spatial grating B of the grating filter 102 used in the scanning optical device having a relatively low resolution (for example, 500 dpi or less).
Is set so that the focus position deviation Δl does not normally exceed the depth of focus of this scanning optical device, that is, about 2.0 mm. Therefore, the pitch error Δd ₂ is expressed by the relational expression (10),
From (11), it is necessary to satisfy the following conditions. This condition is also a condition under which the moire fringes 35 with clear contrast can be obtained because the distances l ₁ and l ₂ do not become too small.

−0.63 μm <Δd ₂ <0 Also, the focus position deviation Δl due to the pitch error Δd ₂ should not exceed the depth of focus of the scanning optical position of high resolution (for example, 600 dpi), that is, about 0.2 mm. , The pitch error Δd ₂ satisfies −6.53 μm <Δd ₂ <0 from the relational expressions (10) and (11). Further, in order to improve the reliability and to suppress the focus position deviation Δl due to the pitch error Δd ₂ to about 0.02 mm, the pitch error Δd ₂ is calculated by the relational expression (10).
From (11), −0.06 μm <Δd ₂ <0. If the focus position deviation Δl due to the pitch error Δd ₂ can be suppressed to about 0.02 mm, the permissible mounting error of the photoelectric conversion element 105 and the like can be increased,
It is practically effective.

(Explanation of Reduction Optical System) In order to improve the detection accuracy of defocus, it is preferable to increase the inclination angle of the moire fringes with respect to the defocus amount. For that purpose, the inclination angle of the spatial grid of the second filter may be set smaller than the spatial grid of the first filter. However, simply reducing the inclination angle increases the pitch of the moire fringes, reduces the number of moire fringes formed on the light receiving surface of the photoelectric conversion element, and reduces the amount of information to the photoelectric conversion element. Detection is more likely to occur. Also, the light receiving surface of the photoelectric conversion element may be too small compared to the size of the moire fringes generated by the two lattice filters. In this case, there is a problem that the loss of the light amount is large and the contrast is hardly obtained. Therefore, in order to solve these problems, the first embodiment includes the cylindrical lenses 103 and 104 forming a reduction optical system.

The cylindrical lenses 103 and 104 are
The cylindrical lens 103 has a light condensing action only in the main scanning direction b, and the cylindrical lens 104 has a light condensing action only in the sub scanning direction c. Therefore, the laser beam L transmitted through the two grating filters 101 and 102 is condensed by the cylindrical lenses 103 and 104, and then forms moire fringes 35 on the light receiving surfaces 105a and 105b of the photoelectric conversion element 105. Even if the inclination angle of the spatial grating of the two grating filters 101 and 102 is reduced to improve the detection accuracy of defocus, the moire fringes are reduced by the cylindrical lenses 103 and 104 and the photoelectric conversion element 105 The light reaches the light receiving surfaces 105a and 105b.
Therefore, the small-sized photoelectric conversion element 105 can improve the detection accuracy of the defocus without losing the light amount of the moire fringes.

As described above, by forming the reduction optical system with the two cylindrical lenses 103 and 104, the reduction magnification of the moire fringes in the main scanning direction and the sub-scanning direction can be easily changed. If the reduction magnifications in the main scanning direction and the sub-scanning direction can be made different, the photoelectric conversion element 1
In accordance with the size of the light receiving surfaces 105a and 105b, moiré fringes of an appropriate number and size can be projected, which is desirable. The same effect can be obtained even if such a reduction optical system is configured by an anamorphic lens having different magnifications in the main scanning direction and the sub-scanning direction. In this case, however, the main scanning direction and the sub-scanning direction are simultaneously performed. Since adjustment must be performed, positioning with respect to the light receiving surfaces 105a and 105b becomes more difficult than when two cylindrical lenses are used. The light receiving surface 105 of the photoelectric conversion element 105
The reduction optical system may be constituted by a single lens having a positive refractive power as long as an appropriate moiré fringe can be projected on a and 105b.

Further, a detailed description will be given using numerical values.
The pitch d ₁ of the spatial grating A is 125 μm, and the spatial grating B is
250μm pitch dimension d ₂ of the 4 times a minute inclination angle α of the spatial grating B, the distance from the in-focus position to the spatial grid A l ₁
Is 40 mm, and the distance l ₂ from the focus position to the spatial grid B is 80 mm, the following numerical values are obtained from the relational expression (5) for the inclination of the moiré fringes 35.

[Cosα-｛(l₁d_Two) / (L
_Twod₁)｝] / Sin α = −0.035 Therefore, tan φ = −0.035, and φ = −2
[Degree]. Thereby, the inclination of the moiré fringes 35 becomes −
88 [degrees]. On the other hand, the photoelectric conversion element 1
Distance to 05_ThreeThen, the pitch of the moiré fringes 35
The dimension P is f = 1_Threed ₁/ L₁Therefore, the relational expression
From (6), the following numerical values are obtained.

P = (f / sin α) × cos (φ−α)
= 3.56 [mm] Here, when a two-segment photodiode having a width of 3 mm and a height of 1 mm is used as the photoelectric conversion element 105, if the laser beam scanning optical device is assumed to be a cylindrical lens 10
Without 3,104, the pitch dimension P is 3.56 mm
Only one moire fringe can be received by the photoelectric conversion element 105. Moire fringes generated under the above conditions are as follows:
The height at the light receiving surface position of the photoelectric conversion element 105 is about 3 mm. However, since the height of the photoelectric conversion element 105 is 1 mm, 2/3 of the height of the moiré fringes deviates from the light receiving surface, and the light amount is correspondingly lost. Further, the laser beam is caused by an optical system error or a manufacturing error of the grating filter or the photoelectric conversion element support portion or a temporal change, and the like.
, The lattice filter 101 becomes the lattice filter 10
2, the moire fringes move in parallel with the main scanning direction b while maintaining the pitch dimension and the tilt angle, and one moire fringe moves along the edge of the light receiving surface. It moves to the center and the detection ability becomes unstable. Usually, in order to stably detect defocus, it is preferable that at least three or more moire fringes are formed on the light receiving surface.

On the other hand, when the laser beam scanning optical apparatus has the cylindrical lenses 103 and 104 of the reduction optical system, the magnification of the cylindrical lens 103 is at least three or more moire fringes on the light receiving surface 10 of the photoelectric conversion element 105.
5a and 105b. For example, the magnification of the cylindrical lens 103 is set to three times. Usually, in order to stably detect the defocus, it is preferable that at least three or more moire fringes are formed on the light receiving surface. In addition, a cylindrical lens 1
The magnification of 04 is selected such that the height of the moire fringes at the light receiving surface position is equal to or less than the height of the photoelectric conversion element.

FIG. 11 shows the contrast of the moire fringes projected on the light receiving surfaces 105a and 105b when the polygon rotation speed is about 20,000 and the laser power at the light receiving surface position is about 1 mW. The output current is converted into a voltage and is represented by a voltage difference. In the figure, solid line 106a
Has a reduction optical system, and a dotted line 106b indicates a case without a reduction optical system. The contrast of the moire fringes is about 0.2 V as the voltage difference when the reduction optical system is not provided, while the contrast of the moire fringes is 0.5 to 1.0 V when the reduction optical system is provided (FIG. 11). In the case of
5V).

(First Phase Difference Detection Structure and Moiré Fringe Selection Means) Next, the moiré fringes 3 reduced by the reduction optical system
The method of detecting the inclination of the moire fringes 35 when a plurality of moire fringes exist on the light receiving surfaces 105a and 105b as shown in FIG. 5 will be described with reference to FIGS. Whether the focal position of the laser beam is in the front focus state, the back focus state, or the in-focus state is determined by the light receiving surface 105a on which the moiré fringes 35 are projected.
And the peak value of the output waveform of the light receiving surface 105b. From this determination result, the moving direction of the focusing lens 3 is determined, and the control signal is transmitted to the stepping motor 2 via the focusing lens drive control unit 26.
Send to 1. The stepping motor 21 rotates in either the forward or reverse direction to move the focusing lens 3 by a predetermined amount on the optical axis. When the lens 3 moves away from the laser diode 1, the focal point is adjusted backward, and when the lens 3 moves closer, the focal point is adjusted forward. The amount of one movement of the lens 3 is set to a predetermined value at which the focal point moves by about 0.01 mm, and such movement is repeated until the focusing state is reached.

As described above, in the first embodiment, the moire fringes 35 in the focused state are orthogonal to the main scanning direction b (FIG. 12).
The beam detector 100 is set so that the moire fringes 35 in the front focus state tilt rightward (see FIG. 13), and the moire fringes 35 in the rear focus state tilt left (see FIG. 14).

12 to 14, 107a, 10a
7b shows output waveforms obtained by converting output currents of the light receiving surfaces 105a and 105b into voltages. Light receiving surface 105
The dark portions of the moire fringes 35 straddling a and 105b correspond to the valleys of the output waveforms 107a and 107b, and the bright portions of the moire fringes 35 correspond to the peaks of the output waveforms 107a and 107b. And, in which state the moiré fringe is in the above state,
The determination can be made based on the phase difference between the bright portions of the moire fringes straddling the light receiving surfaces 105a and 105b. That is, the light receiving surface 10
Output waveform 107a of 5a and output waveform 1 of light receiving surface 105b
When the phase difference of the peak value of 07b is 0 (see FIG. 12), the focus state is set, and the output waveform 107a is changed to the output waveform 107b.
When the phase is further delayed by the phase difference ΔT1 (see FIG. 13), the front focus state is determined, and when the output waveform 107a is ahead of the output waveform 107b by the phase difference ΔT2 (see FIG. 14), the rear focus state is determined.

Further, a method of processing an output waveform will be described in detail with reference to a control circuit block diagram shown in FIG. The electric circuit shown in FIG. 15 includes variable amplifiers 202 and 211, delay amplifiers 203 and 212, comparators 204 and 213, flip-flops 205 and 214, and AND elements 206, 209, and 2.
15, timers 207 and 216, OR element 208, programmable timer 219, microcomputer 220, peak hold circuits 221 and 222, difference circuit 223, microcomputer 22
4 and delay circuits 225 and 226. The comparators 204 and 213 and the flip-flop 205,
At 214, the analog output waveforms from the light receiving surfaces 105a and 105b are converted into digital signals, and
6, 209, 215, the light receiving surface 105
This is because the output waveforms from a and 105b can be processed as digital signals, and a highly reliable control system can be obtained.

After the output waveform S1 of the light receiving surface 105a is amplified by the variable amplifier 202 and the delay amplifier 203,
Each of the waveforms S2 and S3 is input to the comparator 204. The comparator 204 compares the waveforms S2 and S3, and outputs the output waveform as a digital signal S4. Similarly,
After the output waveform S5 of the light receiving surface 105b is amplified by the variable amplifier 211 and the delay amplifier 212, the respective waveforms S6 and S7 are input to the comparator 213. Comparator 21
3 compares the waveforms S6 and S7 and outputs the output waveform as a digital signal S8. By these processes, the output waveforms S1 and S5, which are analog signals, are digitized, and the peaks and valleys of the analog waveform correspond to the H level (High level) or L level (Low level) switching points of the digital signals S4 and S8. (See FIG. 22). Signal S
4 and S8 are input to flip-flops 205 and 214 via delay circuits 225 and 226 (described later), respectively.

By the way, as shown in FIG. 16, the spot Lb of the laser beam L is set so that the center thereof is usually aligned with the center of the photoelectric conversion element 105 (Lb _{1 in the} figure).
reference). In this case, as shown in FIG.
Since the peak values of 7a and 107b are substantially equal, the detection of the phase difference ΔT is stable. However, due to changes in the environment (temperature and humidity), the optical path of the laser beam L may shift in the sub-scanning direction as shown in FIG. 16 (see Lb ₂ and Lb _{3 in the} figure) _. When such an optical path shift occurs, when the spot is located at the position of Lb ₂ , FIG.
Peak value of the output waveform 107b as shown in 8 is lowered, if the spot is located at the position of the Lb _3, since the peak value of the output waveform 107a is lowered as shown in FIG. 19, the phase difference ΔT detected not There is a worry about stability.

Therefore, the first embodiment is provided with a mechanism for always and stably detecting the phase difference ΔT even if the optical path of the laser beam L is shifted in the sub-scanning direction. That is, the output waveforms S2 and S6 of the variable amplifiers 202 and 211 are input to the peak hold circuits 221 and 222. The peak hold circuits 221 and 222 output the output waveforms S2 and S
6 is held, and the peak value is output as signals S25 and S26. Signals S25, S2
6 is input to the difference circuit 223, and the difference circuit 223 compares the peak value of the signal S25 with the peak value of the signal S26, and inputs the output signal S27 to the microcomputer 224.

The microcomputer 224 determines the gain of each of the variable amplifiers 202 and 211 according to the output signal S27. At this time, the amplification factors are variable amplifiers 202 and 211.
Are the values at which the peak values of the waveforms S2 and S6 output from are substantially equal. This amplification factor is output as signals S28 and S29. The signals S28 and S29 are respectively supplied to the variable amplifier 20.
2, 211, and the gain of the variable amplifiers 202, 211 is adjusted.

By these processes, even if the optical path of the laser beam L is shifted in the sub-scanning direction, the output waveforms 107a, 107
07b, the variable amplifiers 202, 2
11, the peak values of the output waveforms S2 and S6 can be made substantially equal, and the detection of the phase difference ΔT can always be performed in a stable state.

Next, a description will be given of moire fringe selecting means for selecting a moire fringe for detecting an inclination from a plurality of moire fringes projected on the light receiving surfaces 105a and 105b.
The moiré fringe selecting means is not always necessary, but if the moiré fringe selecting means is not provided, the laser beam L
Is shifted in the sub-scanning direction, the photoelectric conversion element 105
The moire fringes projected on the light receiving surfaces 105a and 105b move in the main scanning direction, a part of the moire fringes deviates from the light receiving surface, the waveform of the output signal is distorted, and the state of the moire fringes is stably determined. May not be possible. Therefore, moiré fringe selection means selects moiré fringes located at desired positions on the light receiving surfaces 105a and 105b so that the state of the moiré fringes can be determined stably.

As shown in FIG. 15, the laser beam is
When the light enters the S optical sensor 17, the SOS optical sensor 1
7 outputs a beam detection signal S10. This beam detection signal S10 is input to the programmable timer 219. The programmable timer 219 is connected to the microcomputer 22
The count value is set by the 0 data bus S11. The programmable timer 219 starts counting at the rising edge of the beam detection signal S10, counts up based on the set value from the microcomputer 220, and outputs the output signal S12 to the flip-flops 205 and 2
By inputting to 14 clear inputs, each flip-flop is cleared and set to L level. The cleared flip-flops 205 and 214 are set so as to change from L level to H level at the falling edges of the respective clock input signals S4 and S8. That is, by setting the count value of the programmable timer 219 freely by the microcomputer 220, the pulse width of the output signal S12 can be changed, and a desired moire fringe for detection can be selected from a plurality of moire fringes. First
In the embodiment, the moiré fringe 3 projected on the light receiving surface 105a is used.
5 shows an example in which the shape of the stripe of the second bright part from the left is determined (see FIG. 22).

As described above, the beam detection signal S10 output from the SOS optical sensor 17 is also used as the count start signal of the programmable timer 219 of the moiré fringe selecting means, thereby simplifying the apparatus and reducing the cost. Can be achieved. Further, the position of the SOS optical sensor 17 is fixed with respect to the photoelectric conversion element 105, and even if the optical path of the laser beam is shifted in the sub-scanning direction, the rise of the detection signal S10 output from the SOS optical sensor 17 is increased. Edge positions do not vary. Therefore, the timing of the count start of the programmable timer 219 does not shift, and moire fringe selecting means with high selection accuracy can be obtained.

The above-mentioned moiré fringe selecting means is provided with an SOS
Although the optical sensor 17 for use is used, the present invention is not limited to this, and a photoelectric conversion element 113 dedicated to moiré fringe selection means may be used as shown in FIGS. The photoelectric conversion element 113 is a photoelectric conversion element
5, the laser beam L condensed by the cylindrical lenses 103 and 104, which are reduction optical systems, is incident on the light receiving surface 113a. In particular, the photoelectric conversion element 113 illustrated in FIG. 21 is provided on the same substrate 115 together with the photoelectric conversion element 105.

In FIG. 15, the flip-flop 205 cleared by the output signal S12 outputs the signal S13 from the Q output at the falling edge of the clock input signal S4. Similarly, flip-flop 214
Is caused by the falling edge of the clock input signal S8.
The signal S14 is output from the Q output. The focus state can be detected by determining whether the time difference ΔT between the rises of the signal S13 and the signal S14 is positive, negative, or zero. Therefore, next, a method of determining whether the time difference ΔT is positive, negative, or zero will be described.

The flip-flop 205 outputs the Q output signal S1
3 and its inverted output signal S15, and the flip-flop 214 outputs the Q output signal S14 and its inverted output signal S15.
16 is output. Therefore, the inverted output signal S15 of the flip-flop 205 and the Q output signal S14 of the flip-flop 214 are input to the AND element 206, and the AND output signal S17 is output. Similarly, flip-flop 205
And the inverted output signal S16 of the flip-flop 214 are input to the AND element 215 to output the logical product output signal S18.

In the case of the front focus state shown in FIG.
The AND output signal S17 of the AND element 206 is a short pulse having a pulse width ΔT. On the other hand, the logical product output signal S18 of the AND element 215 maintains the L level. That is, an output of (S17, S18) = (H, L) is obtained.
In the case of the back focus state, the output signal S17 maintains the state of the L level, and the output signal S18 is a short pulse having a pulse width ΔT. That is, (S17, S18) = (L,
H) is obtained.

Further, in the case of the focused state, the AND element 20
6 and 215, the pulse width ΔT of the output signal S17 or S18 is short.
Neither output of the ND elements 206, 215 becomes H level. That is, an output of (S17, S18) = (L, L) is obtained. The logical product output signals S17 and S18 of the AND elements 206 and 215 are output to the output signals S19 and S20 via the timers 207 and 216, respectively.
08 to output the OR signal S21. The timers 207 and 216 are for increasing the pulse width ΔT of the short pulse signals of the logical product output signals S17 and S18 in order to facilitate the waveform processing in the OR element 208.

The logical sum output signal S21 is supplied to the AND element 209.
And an output signal S22 from a port of the microcomputer 220 is input to the other input terminal of the AND element 209. Thus, control by the microcomputer 220 is enabled. The logical product output signal S23 of the AND element 209 is a motor ON signal. Timer 216
Is the motor forward / reverse rotation signal.

As described above, by providing the moiré fringe selecting means for selecting the moiré fringe for detecting the inclination,
Even if the laser beam shifts in the sub-scanning direction and the moiré fringes move in the main scanning direction b, the moiré fringe selector can always detect the inclination of the moiré fringe located at the center of the light receiving surface and stably generate the moiré fringes. The state can be determined.

The above focusing operation is executed before the start of printing and during the non-printing time between pages during continuous page printing. According to the first embodiment, it is possible to determine the front focus state or the back focus state, so that the direction in which the focusing lens 3 is moved can be determined in advance, and the focusing operation can be performed in a very short time.
In addition, when the focusing operation is performed between pages, the time interval of the focusing operation is short, so that the defocus amount due to an environmental change or the like during the operation is small, and the defocus can be corrected by moving the lens by about one step. Therefore, the focusing operation can be reliably performed even in a very short time between pages.

(Configuration and Function of Delay Circuits 225 and 226) By the way, usually, the initial state (best focus)
Accordingly, the photoelectric conversion element 105 is adjusted in accordance with the inclination of the moiré fringes 35.
Of the components 101 to 105 of the beam detector 100
It is difficult to adjust the angle to the optimum angle with the dimensional accuracy described above.
If the peak positions of the output waveforms of the light receiving surfaces 105a and 105b can be set to be equal in the initial state, the signal processing becomes easy.

Therefore, in the first embodiment, as shown in FIG. 23, even if the moiré fringes 35 are inclined rightward in the initial state, the light receiving surface 105 using the delay circuits 225 and 226 is used.
Electrical processing is performed so that the peak positions of the output waveforms a and 105b become equal, so that the in-focus state can be considered. That is, when the moiré fringes 35 are inclined rightward, as shown in FIG.
The shift of the peak position occurs between the output waveforms 107a and 107b of b. This time difference ΔT4 is applied to the delay circuit 225,
226, the peak position of the output waveform 107b is shifted to the peak position of 107a, and the signals S4 and S4 are shifted.
8 is input to the flip-flops 205 and 214 without a time difference. As a result, the flip-flop 20
Signals after 5,214 can be processed as an apparently focused state.

Also, depending on the dimensional accuracy and mounting of the components of the scanning optical device, as shown in FIG.
The inclination of 5 varies. Moiré fringe 3 in the initial state
When the actual moiré fringe 35 has the inclination indicated by the dotted line with respect to the target inclination of 5 (indicated by a solid line), the actual output waveform 107a (indicated by a dashed line) Output waveform 107a '(indicated by a dotted line) has a time difference ΔT
Yields 5. Therefore, by adjusting the time difference ΔT5 by adjusting the delay time of the delay circuits 225 and 226,
The peak position of the output waveform 107a 'can be shifted to the peak position of 107a to be zero. As a result, the inclination of the moiré fringes 35 can be detected with higher accuracy.

FIG. 27 shows a specific configuration example of the delay circuits 225 and 226. Inductors L1, L
, L3,... Are connected in series, and switch elements SW1, SW2, SW3, S
By turning on or off any one of W4,... By the microcomputer 220, the delay circuits 225, 226
Delay time can be adjusted. For example, when the scanning optical device is shipped, the output waveforms 107a and 107b of the light receiving surfaces 105a and 105b are monitored by an oscilloscope.
The switch elements SW1, SW2,... Of the delay circuits 225, 226 are turned on and off so that the time differences ΔT4 and ΔT5 become zero.

As described above, the delay circuits 225 and 22
If 6 is used, there is no large difference between the peak values of the output waveforms 107a and 107b, so that stable control can be performed. (Adjustment of the tilt of the photoelectric conversion element 105) The delay circuits 225 and 226 are used as means for making the peak positions of the output waveforms of the light receiving surfaces 105a and 105b equal in the initial state (best focus). However, the present invention is not limited to those electrically processed. For example, using the adjustment jig 400 having the structure shown in FIG. 28, the inclination of the photoelectric conversion element 105 is changed to an optimum angle in accordance with the inclination of the moire fringes 35, and the peak positions of the output waveforms of the light receiving surfaces 105a and 105b are equal. May be set.

That is, the photoelectric conversion element 105 is attached to the adjustment jig 400 such that the photoelectric conversion element 105 can move in the tilt rotation direction of the moire fringes. The adjustment jig 400 includes a fixed base 401 and a sensor holder 409. Fixed base 401
Has a U-shape, and a pair of leaf springs 402, 40
3 are provided facing each other, a shaft hole 404 is provided in the center, and screw holes 405 and 406 are provided in the upper part. Screws 407 and 408 are screwed into the screw holes 405 and 406, respectively. The sensor holder 409 has a shaft 4
The shaft 410 is fitted in a shaft hole 404 provided in the fixed base 401. The photoelectric conversion element 105 is fixed to the front center portion of the sensor holder 409 with, for example, a screw or an adhesive.

As shown in FIG. 29, leaf springs 402 and 40
Numerals 3 each elastically contact the lower surface of the sensor holder 409 to support the sensor holder 409, and screws 407, 408
The tip of the button presses the upper surface of the sensor holder 409. The amount of feed of the screws 407 and 408 is
The fulcrum is used as a fulcrum and the photoelectric conversion element 1
05 can be changed to an optimum angle. The feed amount is adjusted by a not-shown micrometer or the like.

With the above configuration, as shown in FIG. 30, the inclination of the photoelectric conversion element 105 can be optimized according to the inclination of the moire fringes without strictly limiting the dimensional accuracy of the components 101 to 105 of the beam detector 100. Angle can be set at an appropriate angle, and the initial state can be easily set. Further, since the peak positions of the output waveforms of the light receiving surfaces 105a and 105b can be set to be equal in the initial state, the signal processing is also facilitated.

Further, a detailed description will be given using numerical values.
The pitch d ₁ of the spatial grating A is 125 μm, and the spatial grating B is
250μm pitch dimension d ₂ of the 4 times a minute inclination angle α of the spatial grating B, the distance from the in-focus position to the spatial grid A l ₁
Is 40 mm, and the distance l ₂ from the focus position to the spatial grid B is 80 mm, the inclination of the moiré fringes is calculated from the relational expression (5) as follows: [cos α − ｛(l ₁ d ₂ ) / (l ₂ d ₁₎ )｝] / Sinα
= −0.035. Therefore, tan φ = −0.035, and φ =
-2 [degrees]. Thereby, the inclination of the moiré fringe is −
It will be 88 degrees.

Here, due to a component processing accuracy error, the minute inclination angle α of the spatial grid B is 3.8 degrees, the distance l ₁ from the focus position to the spatial grid A is 40.2 mm, and the spatial grid B is When the distance l ₂ until is to become 79.8Mm, the inclination of the moire fringes from equation (5), [cosα - { (l 1 d 2) / (l 2 d 1)}] / sinα
= −0.147. Therefore, tan φ = −0.147, and φ =
It becomes -8.4 [degree]. 5. For design value -2 [degrees]
If the inclination of the photoelectric conversion element 105 cannot be changed to an optimum angle in accordance with the inclination of the moire fringes, the light receiving surfaces 105a and 105b will change.
The peak positions of the respective output waveforms differ from each other, and the setting of the initial state and the signal processing become complicated.

Further, inside the sensor holder 409, an electrical board on which electronic components of an output signal processing circuit for detecting a phase difference of moiré fringes is mounted is held. in this way,
By integrally providing the photoelectric conversion element 105 and the electrical board on which the control circuit is mounted, there is no need to route a large number of signal lines output from the photoelectric conversion element 105, and the beam detector 100 is very easy to assemble. can do.

On the other hand, the photoelectric conversion element 105 and the electrical component board of the output signal processing circuit may be formed separately. In this case, many signal lines output from the photoelectric conversion element 105 need to be routed from the sensor holder 409, but there is an advantage that the electronic components on the electrical board can be protected from heat generation of the photoelectric conversion element 105. Sensor holder 40
9, the photoelectric conversion element 105 to be used is used.
Any of the above configurations may be adopted in consideration of the heat generation amount and the heat resistance of the electronic component.

(Second phase difference detecting structure and moiré fringe selecting means) The phase difference detecting structure and moiré fringe selecting means are not limited to those described above. A phase difference detection configuration and moiré fringe selection means may be used. In the second phase difference detecting configuration and the moiré fringe selecting means, whether the focal position of the laser beam is in the front focus state,
Whether the back focus state or the in-focus state is determined based on the phase difference between the output waveform of the light receiving surface 105a on which the moiré fringes 35 are projected and the valley (dark portion of the moire fringes) of the output waveform of the light receiving surface 105b.
The moiré fringes 35 in the focused state are orthogonal to the main scanning direction b (see FIG. 31), the moiré fringes 35 in the front focus state rotate rightward and tilt to the right (see FIG. 32), and the moiré fringe in the back focus state. The beam detector 100 is set so that the stripe 35 rotates to the left and tilts to the left (see FIG. 33).

In FIGS. 31 to 33, the state of the moire fringes can be determined by the phase difference between the dark portions of the moire fringes straddling the light receiving surfaces 105a and 105b. That is, when the phase difference between the troughs of the output waveform 107a of the light receiving surface 105a and the output waveform 107b of the light receiving surface 105b is 0 (see FIG. 31), the in-focus state and the output waveform 107b
Is determined as a front focus state when the output waveform 107a is ahead of the output waveform 107a by a phase difference ΔT1 (see FIG. 32), and is determined as a rear focus state when the output waveform 107a is advanced from the output waveform 107b by a phase difference ΔT2 (see FIG. 33). I do.

Further, a method of processing an output waveform will be described in detail with reference to a control circuit block diagram shown in FIG. The electric circuit shown in FIG. 34 includes the amplifiers 230 and 231 and the delay amplifier 2
03, 212, comparators 204, 213, flip-flops 205, 214, 218, AND elements 206, 20
9, 215, timers 207, 216, OR element 208,
It comprises a comparator 217, a programmable timer 219 and a microcomputer 220.

After the output waveform S1 of the light receiving surface 105a is amplified by the amplifier 230 and the delay amplifier 203, the respective waveforms S2 and S3 are input to the comparator 204. The comparator 204 compares the waveforms S2 and S3, and outputs the output waveform as a digital signal S4. Similarly, the output waveform S5 of the light receiving surface 105b is amplified by the amplifier 231 and the delay amplifier 212, and then the respective waveforms S6, S5
7 is input to the comparator 213. The comparator 213 has a waveform S
6 and S7, and outputs the output waveform as a digital signal S8.

Next, a description will be given of moire fringe selecting means for selecting a moire fringe for detecting an inclination from a plurality of moire fringes projected on the light receiving surfaces 105a and 105b.
The amplified waveform S2 output from the amplifier 230 is compared with the comparator 2
Input to 17. The comparator 217 is set to be at the H level when the voltage of the waveform S2 becomes higher than the reference voltage _Vref of the comparator 217. The output waveform S9 of the comparator 217 is input to the flip-flop 218. further,
The output waveform S10 of the flip-flop 218 is input to the programmable timer 219. The count value of the programmable timer 219 is set by the data bus S11 of the microcomputer 220.

The programmable timer 219 starts counting at the rising edge of the output waveform S10, counts up based on the set value from the microcomputer 220, and outputs the output signal S12 to the flip-flops 205, 2
By inputting to the clear inputs 14 and 218, each flip-flop is cleared and set to L level. The cleared flip-flops 205, 214, and 218 are set so as to change from L level to H level at the rising edges of the respective clock input signals S4, S8, S9. That is, the programmable timer 219
Is set by the microcomputer 220 as desired, the pulse width of the output signal S12 is changed, and a desired moiré fringe for detection can be selected from a plurality of moiré fringes. In the first embodiment, an example has been described in which the shape of the second darkest fringe fringe of the moiré fringe 35 projected on the light receiving surface 105a is determined (see FIG. 35).

The flip-flop 205 cleared by the output signal S12 outputs the signal S13 from the Q output at the rising edge of the clock input signal S4. Similarly, the flip-flop 214 outputs the clock input signal S
At the rising edge of 8, the signal S14 is output from the Q output. The focus state can be detected by determining whether the time difference ΔT between the rises of the signal S13 and the signal S14 is positive, negative, or zero. The method of determining whether the time difference ΔT is positive, negative, or 0 has been described in detail in the first phase difference detection mechanism, and will not be described.

(Modification of Photoelectric Conversion Element and Reduction Optical System)
In the first embodiment, the two-part photodiode 105 having two light receiving surfaces is used as the photoelectric conversion element.
The number of photoelectric conversion elements is not limited to this, and the number of photoelectric conversion elements is arbitrary as long as at least two light receiving surfaces can be secured. For example, as shown in FIG. 36, photodiodes 116a and 116a each having only one light receiving surface.
6b and 116c may be used in combination.

As shown in FIG. 37, two linear line sensors 116d and 116e are used as photoelectric conversion elements.
May be installed at positions distant upward and downward in the sub-scanning direction c from the rotation center of the moiré fringes, respectively, in parallel with the main scanning direction b. In this case, two lattice filters 1
After being condensed by the cylindrical lenses 103 and 104, the laser beam L transmitted through 01 and 102 forms Moire fringes straddling the linear line sensors 116d and 116e. Then, the two linear line sensors 116
By detecting the distance between the respective peak values of the output waveforms d and 116e, it is possible to know the change in the slope of the moiré fringe. Alternatively, as shown in FIG. 38, by using an area CCD as the photoelectric conversion element, the amount of information may be increased and the detection error of the focus position shift may be reduced. This is because the pitch interval of the bright portions of the moire fringes can be measured in a plurality of lines, and the average of the measured values obtained can be obtained.

As the reduction optical system, a positive lens 117 may be used as shown in FIG. Positive lens 11
7 has a light condensing function in the main scanning direction b and the sub-scanning direction c, so that the laser beam L transmitted through the two grating filters 101 and 102 is condensed by the positive lens 117 and then received by the light receiving surface of the photoelectric conversion element 105. Moire fringes are formed on 105a and 105b. The positive lens 117 may be an anamorphic lens having different magnifications in the main scanning direction b and the sub-scanning direction c.

[Second Embodiment, FIGS. 40 to 45] As described in the first embodiment, when the optical path of the laser beam is shifted in the sub-scanning direction due to a change in environment (temperature, humidity) or the like, the photoelectric conversion is performed. The peak values of the two output waveforms from the conversion element are different (see FIGS. 18 and 19).
There is a concern that the detection of the phase difference ΔT becomes unstable. The first embodiment employs a mechanism that makes the peak values of two output waveforms substantially equal by using a variable amplifier, a peak hold circuit, a difference circuit, and the like.

In the second embodiment, a mechanism different from that of the first embodiment is employed, so that the phase difference ΔT can always be detected stably even if the optical path of the laser beam is shifted in the sub-scanning direction. The scanning optical device will be described. Second
The laser beam scanning optical device of the embodiment has the same structure as that of the device of the first embodiment except for a beam detector and a control circuit, and thus a detailed description thereof will be omitted.

As shown in FIG. 40, the beam detector has four photoelectric conversion elements 118a, 118b, 118c, 118
d. Photodiodes or the like are used as the photoelectric conversion elements 118a to 118d, and are respectively installed at positions separated upward and downward in the sub-scanning direction c from the rotation center of the moiré fringe, in parallel with the main scanning direction b. This beam detector is disposed near an optically substantially equivalent position to the surface to be scanned, and the spatial grating A is parallel to the main scanning direction b of the laser beam L, and the spatial grating B is inclined by a small angle. .
After being condensed by the cylindrical lenses 103 and 104, the laser beam L transmitted through the two grating filters 101 and 102 forms Moire fringes straddling the photoelectric conversion elements 118a to 118d.

As shown in FIG. 41, normally, in the initial state (best focus), the center of the beam spot Lb of the laser beam L has the photoelectric conversion elements 118b and 118c.
It is set so as to be positioned between (see figure Lb _1). In this case, as shown in FIG.
The output waveforms 119b and 119 of the respective 18b and 118c
The peak value of 9c is high and substantially equal. On the other hand, the output waveforms 119a, 119a,
The peak value of 119d is low. Therefore, if the output waveforms 119b and 119c having high and substantially equal peak values are selected, the phase difference ΔT can be detected stably.

Then, due to a change in the environment, the optical path of the laser beam L is shifted in the sub-scanning direction as shown in FIG.
When the beam spot is shifted to the position of Lb ₂ , FIG.
As shown in FIG. 3, if the output waveforms 119a and 119b having high and substantially equal peak values are selected, the phase difference ΔT can be detected stably. Also, as shown in FIG.
When the beam spot is shifted to the position of the Lb ₃ is 4
As shown in FIG. 4, if the output waveforms 119c and 119d having high and substantially equal peak values are selected, the phase difference ΔT can be detected stably.

Further, a method of processing the output waveforms 119a to 119d will be described in detail with reference to a control circuit block diagram shown in FIG. The electric circuit shown in FIG.
233, peak hold circuits 235a, 235b, 23
5c, 235d and switch element group SW (SW5 to SW
10) and the like.

Output waveforms 119a to 119d from photoelectric conversion elements 118a to 118d are input to peak hold circuits 235a to 235d, respectively. The peak hold circuits 235a to 235d output the output waveforms 119a to 119
Each peak value (maximum voltage value) of d is held, and the peak value is input to the microcomputer 220. Microcomputer 22
0 selects two adjacent photoelectric conversion elements having a high peak value, and only the output waveforms of these two photoelectric conversion elements
The control signal S32 is output so as to be input to the delay amplifiers 203 and 212 and the delay amplifiers 203 and 212.

The control signal S32 is input to the switch element group SW to turn on the individual switch elements SW5 to SW10,
Control off. For example, when the beam spot is shifted to the position of Lb ₂ (see FIG. 41), the peak values of the output waveforms 119a and 119b are high (see FIG. 43), and the microcomputer 220 selects the photoelectric conversion elements 118a and 118b. ,
The switch elements SW5, SW7 are turned on by the control signal S32, and the switch elements SW6, SW8, SW9, SW10
Turn off. As a result, the output waveform 119a from the photoelectric conversion element 118a is output to the amplifier 232 and the delay amplifier 20.
3 and output waveform 1 from the photoelectric conversion element 118b.
19b is input to the amplifier 233 and the delay amplifier 212. Thereafter, by the same processing as described in the first embodiment, the phase difference ΔT between the peak values of the two output waveforms 119a and 119b is measured, and a focus shift is detected.

As described above, even if the optical path of the laser beam L is shifted in the sub-scanning direction, the photoelectric conversion elements 118a to 118a
By selecting two output waveforms having high peak values from the 18d output waveforms 119a to 119d, the phase difference ΔT can be always detected in a stable state.

In the second embodiment, four photoelectric conversion elements are used. However, the present invention is not limited to this. The number of photoelectric conversion elements is arbitrary as long as at least three light receiving surfaces can be secured. is there. For example, as shown in FIG. 46, a three-division photodiode 120 having three light receiving surfaces 120a, 120b, and 120c may be used. Alternatively, as shown in FIG. 47, four linear line sensors 121a, 121b, 121c, 121d may be used. In this case, four linear line sensors 121a to 121a-1
By selecting two output waveforms having high peak values from the respective output waveforms of 21d and detecting the distance between the peak values of the two output waveforms, it is possible to know the change in the slope of the moire fringes.

[Third Embodiment, FIGS. 48 to 50] In the third embodiment, a laser beam scanning optical device capable of detecting the defocus of the laser beam in the sub-scanning direction c will be described. The laser beam scanning optical apparatus according to the third embodiment includes the apparatus according to the first embodiment (particularly, the apparatus including the second phase difference detecting mechanism and the moiré fringe selecting unit) except for the beam detector 150 and the light source control unit. ) Has the same structure as that of FIG.

As shown in FIG. 48, the beam detector 150
Are disposed outside the image area near the position substantially equivalent to the surface to be scanned, and are arranged in the optical axis direction.
152, cylindrical lenses 153 and 154, and a photoelectric conversion element 155. Lattice filter 15
Numerals 1 and 152 have striped spatial gratings A and B, respectively. The spatial grating A is parallel to the sub-scanning direction c, and the spatial grating B is inclined by a small angle. Further, regarding the pitch error of the spatial grating B, the relational expression (1) of the first embodiment is used.
0) and (11) are satisfied.

A cylindrical lens 1 forming a reduction optical system
53 and 154 are cylindrical lenses 153 having a light condensing action only in the main scanning direction b;
Reference numeral 54 has a light condensing function only in the sub-scanning direction c. Therefore, the laser beam L transmitted through the two grating filters 151 and 152 is condensed by the cylindrical lenses 153 and 154, and forms moire fringes on the light receiving surfaces 155a and 155b of the photoelectric conversion element 155.

The photoelectric conversion element 155 is a two-division photodiode having light receiving surfaces 155a and 155b divided into two parts in parallel with the sub-scanning direction c. Here, it is assumed that the laser beams L scanned in the main scanning direction b are continuously irradiated on the grating filters 151 and 152. When the laser beam L is scanned, the moire fringes slightly shift in the main scanning direction b in accordance with the shift of the laser beam L as described in the first embodiment (see FIG. 4).
Therefore, in order to accurately detect the inclination of the moiré fringes, the photoelectric conversion element 155 capable of sampling in a very short time is used.
Is required. However, the photoelectric conversion element 155 having such a function becomes an expensive element, and increases the cost of the laser beam scanning optical device.

Therefore, the laser beam scanning optical apparatus according to the third embodiment employs a fixed-point light emission system in which the laser diode 1 emits light for one pixel and only the laser beam L for one pixel is irradiated on the lattice filters 151 and 152. Adopted.
Since only one pixel is irradiated with the laser beam L, the moire fringes formed on the light receiving surfaces 155a and 155b do not shift minutely, and it is not necessary to use an expensive photoelectric conversion element.

Further, the fixed point light emission method will be described in detail with reference to FIGS. As shown in FIG. 49, the light source control unit includes an SOS detection circuit 271 and a laser diode (LD) drive circuit 272. Note that the control circuit block diagram shown in FIG. 49 is the same as the control circuit block diagram shown in FIG. 34 of the first embodiment except for the SOS detection circuit 271 and the LD drive circuit 272, and therefore its detailed description will be made. Is omitted. A beam detection signal (SOS signal) output from the SOS optical sensor 17 is input to the microcomputer 220 via the SOS detection circuit 271. Further, the microcomputer 22
The LD control signal from 0 is input to the LD drive circuit 272. A programmable timer (not shown) of the LD drive circuit 272 starts counting by the LD control signal. In this programmable timer, a predetermined light emission timing time T1 and a light emission timing time T2 derived based on the rotation speed of the polygon mirror 6 are set by a microcomputer.

Here, the difference between the light emission timing time T1 and the light emission timing time T2 is set to correspond to the LD light emission time for one pixel. As shown in FIG. 50, when the programmable timer counts up and reaches the light emission timing time T1, an LDON signal for autofocus is sent from the LD drive circuit 272 to the laser diode 1, and the laser diode 1 is turned on. Then, after the LD lighting time for one pixel has elapsed, that is, when the light-off timing time T2 has come, the laser diode 1 is turned off. That is, the laser diode 1 is an autofocus LDON.
The signal is emitted outside the image area for a time corresponding to one pixel, and a laser beam for one dot is emitted by the beam detector 150.
Irradiated. In FIG. 50, the image area signal is a signal that controls (turns on and off) the laser diode 1 based on the print data.
This is the period of the S signal.

In the above configuration, the light receiving surfaces 155a, 155
55b each output a signal waveform. From this output waveform, it is possible to detect a light-condensing position shift. That is, by detecting the phase difference between the respective peak values of the output waveform, it is possible to know the change in the inclination of the moiré fringes. Can be determined in front of or behind the surface to be scanned. [Fourth Embodiment, FIGS. 51 to 57] In the laser beam scanning optical device, if the shift of the focusing position always becomes one of the front focus state and the back focus state, the focusing position It is unnecessary to determine whether the camera is in the front focus state or the back focus state.

Therefore, in the fourth embodiment, in the laser beam scanning optical device, the shift of the condensing position is always one of the front focus state and the back focus state.
A configuration for detecting a focused state of a laser beam by a method simpler than that of the embodiment will be described. In the fourth embodiment, an example will be described in which the shift of the condensing position is always in the front focus state. The laser beam scanning optical device according to the fourth embodiment has the same structure as the device according to the first embodiment except for a beam detector and a control circuit, and a detailed description thereof will be omitted.

As shown in FIG. 51, the beam detector 160
Are disposed near optically equivalent positions to the surface to be scanned, and are arranged in the optical axis direction, such as grating filters 161 and 162, cylindrical lenses 163 and 164, and a photoelectric conversion element 165.
It is composed of The grating filters 161 and 162 have striped spatial gratings A and B, respectively. The spatial grating A is parallel to the main scanning direction b of the laser beam L, and the spatial grating B is inclined by a small angle.

A cylindrical lens 1 forming a reduction optical system
Reference numerals 63 and 164 denote cylindrical lenses 163 having a light condensing function only in the main scanning direction b.
Numeral 64 has a light condensing function only in the sub-scanning direction c. Therefore, the laser beam L transmitted through the two grating filters 161 and 162 is condensed by the cylindrical lenses 163 and 164 and forms moire fringes on the light receiving surface of the photoelectric conversion element 165. The photoelectric conversion element 165 is an area CCD,
With a large amount of information, the detection error of the light-condensing position shift can be reduced. This is because the pitch interval of the bright portion of the moire fringes in the main scanning direction can be measured on a plurality of lines, and the average of the obtained measurement values can be obtained.

As shown in FIG. 52, the bright portion of the moiré fringe 35 in the focused state is orthogonal to the main scanning direction b, and as shown in FIG. The beam detector 16 rotates clockwise and tilts to the right.
0 is set. Pitch Q ₂ of the bright part of the Moire fringes 35 of the defocus state, becomes larger than the pitch interval to Q ₁ light portion of the Moire fringes 35 of focusing state, obtaining a difference Q ₂ -Q ₁ pitch interval, this By moving the focusing lens 3 by a predetermined amount on the optical axis according to the difference, a focusing state can be obtained. Then, even if the laser beam is shifted in the sub-scanning direction c and the moire fringes 35 projected on the light receiving surface of the photoelectric conversion element 165 move in the main scanning direction b, the moire fringes 3
The pitch dimension Q ₂ of 5 is maintained, no fear of erroneous detection.

Further, the processing method will be described in detail with reference to the control circuit block diagram shown in FIG. The electric circuit shown in FIG. 54 includes a CCD driver 280, an A / D converter 281,
It comprises a signal processing circuit 282 and a memory 283. The CCD driver 280 and the A / D converter 281 are well known, and a detailed description thereof will be omitted. The output waveform of the photoelectric conversion element 165 is the CCD driver 280 and A
As shown in FIG. 55, the signal is serially input to the signal processing circuit 282 via the / D converter 281.
The signal processing circuit 282, the bright portion of the first Moire fringe signal output to (mountain) and storage address exceeds a threshold level initially _(first address M) in the memory 283. Next, after counting the number of addresses m from when the threshold level is exceeded to when the threshold level is again lowered, the peak address {M ₁ + (m / 2)} of the bright portion of the first moire stripe 35 is stored in the memory 283. To be stored.

[0114] Similarly, the bright portion of the second Moire fringes 35 to (mountains), stores the address exceeds the threshold level (address ₂ M) in the memory 283, the threshold level again threshold level from beyond the After counting the number n of addresses until the number of addresses falls below the maximum value, the peak address {M ₂ + (n / 2)} of the bright portion of the second moiré stripe 35 is stored in the memory 283.
To be stored.

Next, {M ₁ + (m / 2)} − {M ₂ + (n
/ 2)｝ is calculated, and the pitch interval Q of the bright portion of the moire fringe 35 is calculated.
Ask for ₂ . Comparing the pitch to Q ₁ light portion of the pitch Q ₂ and Moire fringes 35 of focusing state determined, the difference (Q ₂ -
Q ₁ ) is obtained. Depending on the sign of the calculated difference (Q ₂ -Q ₁₎ to generate a forward reverse signal of the stepping motor 21, determines the amount of rotation of the stepping motor 21 in accordance with the absolute value of the difference (Q ₂ -Q ₁₎ I do. Next, the signal processing circuit 28
Numeral 2 sends the motor forward / reverse rotation signal and the motor rotation amount signal to the stepping motor 21 via the focusing lens drive control unit 26, and moves the focusing lens 3 by a predetermined amount on the optical axis to bring it into a focused state.

Further, a detailed description will be given using numerical values.
The pitch d ₁ of the spatial grating A is 125 μm, and the spatial grating B is
250μm pitch dimension d ₂ of the 4 times a minute inclination angle α of the spatial grating B, the distance from the in-focus position to the spatial grid A l ₁
Is 40 mm, and the distance l ₂ from the focus position to the spatial grid B is 80 mm, the following numerical values are obtained from the relational expression (5) described in the first embodiment for the inclination of the moiré fringes 35.

[Cosα-｛(l ₁ d ₂ ) / (l
₂ d ₁ )｝] / sin α = −0.035 Therefore, tan φ = −0.035 and φ = −2 degrees. Thus, the inclination of the moiré fringes 35 becomes -88 degrees. On the other hand, if the distance l ₃ from the focus position to the photoelectric conversion element 105 is 90 mm, the pitch dimension Q
_{Since 1} is f = l ₃ d ₁ / l ₁ , the following numerical values are obtained from the relational expression (6) and Q ₁ = P ₁ / cos φ.

Q ₁ = (f / cos φ sin α) × cos (φ−α) = 4.01 [mm] (12) Next, due to a change in the environment or the like, the focal position is Δl = 0.2 m.
m, then φ = −4 from the relational expression (7).
[Degree], the inclination of the moire fringes 35 is -86 [degree].
Becomes The following numerical values are obtained for the pitch dimension Q ₂ of the moiré fringes 35 from the above-mentioned relational expression (6) and Q ₂ = P ₂ / cos φ.

Q ₂ = 3.98 [mm] (13) From the expressions (12) and (13), the focusing position is Δl = 0.2
mm, the pitch size of the moire fringes is 0.03
mm. By detecting this change, a forward / reverse rotation signal of the motor is generated, and the focusing lens 3 is moved on the optical axis by a predetermined amount in a direction away from the laser diode 1 in accordance with the amount of change to thereby shift the focus shifted to the front focus state. Move it backward to bring it into focus.

The pitch interval Q of the bright portion of the moire fringes 35
_As a method for obtaining ₂ , there is a method that uses a peak hold circuit. That is, the signal output shown in FIG. 55 is serially input to the peak hold circuit, and the peak value (maximum voltage value) of the bright portion (mountain) of the first moiré fringe 35 and its address are held, and the address (M ₃ ) is stored in the memory 283. Then, holding the peak value of the light portion of the second Moire fringes 35 and its address, the memory 2 that address the (M ₄ address)
83. Next, (M ₄ −M ₃ ) is calculated, and the pitch interval Q ₂ of the bright portion of the moiré fringes 35 can be obtained.

In the fourth embodiment, the area CCD 165 is used as the photoelectric conversion element. However, the present invention is not limited to this. For example, a linear line sensor 167 may be used as shown in FIG. In this case, the distance between the peak values of the output waveform of the linear line sensor 167 is measured, and the difference between the peak value of the output waveform in the focused state and the distance between the peak values of the output waveform is determined.
Is moved by a predetermined amount on the optical axis to bring it into a focused state. Alternatively, as shown in FIG. 57, a photodiode 168 may be used. In this case, the time from the peak to the peak of the output waveform of the photodiode 168 is measured, the difference from the peak to the peak of the output waveform in the focused state is obtained, and the focusing lens 3 is determined in accordance with the difference. Is moved by a predetermined amount on the optical axis to bring it into a focused state.

[Fifth Embodiment, FIGS. 58 to 61] A laser beam scanning optical apparatus according to a fifth embodiment comprises a beam detector 1
Since it has the same structure as the device of the first embodiment except for the control circuit 70 and the control circuit, detailed description thereof is omitted.

As shown in FIG. 58, the beam detector 170
Are arranged outside the image area near the optically substantially equivalent position to the surface to be scanned, and are arranged in the optical axis direction.
1 and 172 and a photoelectric conversion element 173.
The grating filters 171 and 172 have striped spatial gratings A and B, respectively. The spatial grating A is parallel to the main scanning direction b of the laser beam L, and the spatial grating B is inclined by a small angle. Further, the pitch error of the spatial grating B satisfies the relational expressions (10) and (11) of the first embodiment. The photoelectric conversion element 173 is a four-divided sensor having four divided light-receiving surfaces 173a to 173d, and each of the light-receiving surfaces 173a to 173d outputs a current proportional to the amount of received light.

The laser beam L transmitted through the two grating filters 171 and 172 forms moiré fringes 35 extending over the light receiving surfaces 173a to 173d. The moiré fringes 35 in the focused state are orthogonal to the main scanning direction b (see FIG. 59), whereas the moiré fringes 35 in the front focus state rotate rightward and tilt rightward (see FIG. 60), and The moiré fringe 35 in the focused state is set so as to rotate to the left and tilt to the left (see FIG. 61). .

The four light receiving surfaces 173a to 173d
Output currents Ia, Ib, Ic, Id have the following relationship. (Ia + Ic)-(Ib + Id) = 0 in the focused state, (Ia + Ic)-(Ib + Id) in the front focus state
<0 In the case of the post-focus state, (Ia + Ic)-(Ib + Id)
> 0 These output currents Ia to Id are transferred to the signal processing circuit 24 shown in FIG. 1, and the voltage values Va, V
After being converted into b, Vc, and Vd, the value of (Va + Vc) and the value of (Vb + Vd) are processed by the difference circuit of the signal processing circuit 24 to derive the value of (Va + Vc)-(Vb + Vd). This result is transferred to the control circuit 25, and the control circuit 25
Then, the focus position of the laser beam is determined based on the transferred value. That is, (Va + Vc)-(Vb + Vd)
Is 0, the focus state is determined. If negative, the front focus state is determined. If the focus state is positive, the rear focus state is determined.

[Sixth Embodiment, FIGS. 62 to 66] In the beam detector for detecting moiré fringes, the optical path deviation in the sub-scanning direction of the laser beam greatly affects the detection accuracy. So the sixth
The present embodiment is directed to a laser beam scanning optical device capable of preventing a reduction in defocus detection capability due to an optical path shift in the sub-scanning direction, in addition to the functions and effects of the laser beam scanning optical device of the fifth embodiment. explain. Sixth
The laser beam scanning optical apparatus according to the embodiment has the same structure as the apparatus according to the first embodiment except for the beam detector 180 and an actuator for correcting an optical path deviation, and the like. Is omitted.

As shown in FIG. 62, the beam detector 180
Is disposed at a position optically substantially equivalent to the surface to be scanned, and includes grating filters 181 and 182 and a photoelectric conversion element 183 arranged in the optical axis direction. Lattice filter 18
Reference numerals 1 and 182 each have a triangular striped spatial grid A and a square striped spatial grid B, and the spatial grid A is parallel to the main scanning direction b of the laser beam L. B is inclined by a small angle.

The laser beam L transmitted through the two spatial gratings A and B forms moire fringes on the light receiving surface 183a of the photoelectric conversion element 183. As the photoelectric conversion element 183, a photodiode, a CCD, or the like is used. And the laser beam L
Is shifted in the sub-scanning direction, the laser beam L scans the position where the width of the spatial grating A is different, so that the number of moire fringes 35 formed on the light receiving surface 183a changes.
By detecting the change in the number of moiré fringes by the photoelectric conversion element 183, it is possible to determine the amount of displacement of the optical path of the laser beam L and whether the displacement of the optical path is upward or downward in the sub-scanning direction. Therefore, after the beam detector 180 is moved in the sub-scanning direction by an actuator (not shown) or the like to correct the position, the inclination of the moiré fringe is detected with high accuracy by the beam detector 180 again. Alternatively, a correction table of the moire fringes for the optical path shift in the sub-scanning direction is stored in the signal processing circuit in advance, and the information on the number change of the moire fringes detected by the photoelectric conversion element 183 and the inclination change information are stored in the signal processing circuit. The processing may be performed to derive the inclination of the moiré fringes.

There are various other configurations for preventing a reduction in defocus detection ability due to an optical path deviation in the sub-scanning direction. For example, as shown in FIG. 63, two linear sensors 184a and 184 are used as photoelectric conversion elements.
4b is used in a position separated from the rotation center of the moiré fringe in the sub-scanning direction upward and downward in parallel with the main scanning direction b. The laser beam transmitted through the grating filters 171 and 172 forms moiré fringes 35 extending over the linear sensors 184a and 184b.

In the above configuration, the linear sensor 184
a and 184b respectively output, for example, signal waveforms 185a and 185b shown in FIG. This output waveform 185
a, 185b, it is possible to detect the shift of the condensing position and the shift of the optical path. That is, in the case of a shift of the light condensing position, by detecting a change in the distance Δ between the respective peaks of the output waveforms 185a and 185b, it is possible to know a change in the inclination of the moiré fringes 35. It is possible to determine whether the displacement between the position and the focus position is ahead or behind the surface to be scanned. Further, in the case of an optical path shift, moire fringes 3
By comparing the distance from the position of the rotation center 5 to the peak position of the output waveform 185a with the distance from the position of the rotation center of the moiré fringe 35 to the peak position of the output waveform 185b,
It is possible to determine whether the optical path shift is upward or downward in the sub-scanning direction, and to measure the shift amount.

Further, as shown in FIG.
8, the lattice filters 171 and 172 and the photoelectric conversion element 18
6 and the scanning position detector 187 may be arranged. As the scanning position detector 187, a position detecting element, a CCD or the like is used. A rack is formed on the base plate 188, and an output pinion of a stepping motor meshes with the rack, so that the beam detector can move in the sub-scanning direction.

In the above configuration, the scanning position detector 18
7, the scanning position of the laser beam L in the sub-scanning direction is detected, and the moving direction of the beam detector is determined based on the information on the optical path shift amount in the sub-scanning direction obtained from the scanning position detector 187. Is rotated in either the forward or reverse direction to move the beam detector in the sub-scanning direction by a predetermined amount. After correcting the optical path shift in the sub-scanning direction of the beam detector by this movement, the beam detector detects moiré fringes.

Alternatively, as shown in FIG. 66, a scanning position detector 190 is arranged near the photoelectric conversion element 186, and the scanning position detector 190 detects the scanning position of the laser beam L in the sub-scanning direction. Based on the information on the amount of optical path shift in the sub-scanning direction obtained from the position detector 190, the moire fringes detected by the beam detector are stored in advance using a correction table of the moire fringes for the optical path shift in the sub-scan direction stored in advance. Can be corrected, and the detection of the moiré fringe angle can be more accurately performed.

[Seventh Embodiment, FIGS. 67 to 84] (Overall Configuration of Laser Beam Scanning Optical Device) As shown in FIG. 67, the laser beam scanning optical device of the seventh embodiment is
Generally, a laser diode 501 and a collimator lens 5
02, a cylindrical lens 503, a polygon mirror 504, a toroidal lens 506, and an fθ lens 5
07 and a beam detector 600.

The laser diode 501 is modulated (on / off) by a laser driver 525, and emits a laser beam when turned on. The laser driver 525 is driven based on print data sent from the flash memory 522 via the printer control unit 524.
The laser beam emitted from the laser diode 501 is converged substantially parallel by the collimator lens 502,
After being stopped down in the sub-scanning direction by the cylindrical lens 503, the light reaches the polygon mirror 504.

The polygon mirror 504 is driven to rotate clockwise at a constant speed about a rotation shaft 504a by a motor 505. Laser beam is polygon mirror 504
Are deflected at equal angular velocities on the respective deflection surfaces based on the rotation of the lens, and are incident on the toroidal lens 506 and the fθ lens 507.
The surface tilt correction optical system of the polygon mirror 504 includes a cylindrical lens 503 and a toroidal lens 506. The laser beam emitted from the fθ lens 507 is focused on the photosensitive drum 530 and scans the photosensitive drum 530 in the direction of arrow b. The fθ lens 507 mainly has a function of correcting the laser beam deflected by the polygon mirror 504 at a constant angular velocity to a constant main scanning speed on the surface to be scanned (photosensitive drum 530), that is, a function of correcting distortion. Have.

The photosensitive drum 530 is driven to rotate at a constant speed in the direction of arrow c.
An image (electrostatic latent image) is formed on the drum 530 by the main scanning in the direction and the sub-scanning of the drum 530 in the direction of the arrow c. Further, the laser beam scanning optical device of the seventh embodiment is provided with a moving unit 509 that can move the cylindrical lens 503 in the optical axis direction in order to adjust the shift of the focusing position of the laser beam in the sub-scanning direction. I have. The moving means 509 includes a stepping motor 518, a moving plate 519, and a pedestal 520. The motor shaft 518a of the stepping motor 518 is a screw shaft, and the pedestal 520 on which the cylindrical lens 503 is mounted moves on the moving plate 519 by rotating the motor shaft 518a forward or backward by the autofocus (AF) control unit 521. . Accordingly, the cylindrical lens 503 can move in the front-back direction on the optical axis, and this movement causes the laser beam of the photosensitive drum 5 to move.
The condensing position on 30 is adjusted.

(First Beam Detector) The first beam detector 600 for detecting the in-focus state is located downstream of the laser beam scanning line and outside the image area near the optically substantially equivalent position to the surface to be scanned. It is installed and detects the focused state of the laser beam on the surface to be scanned. More specifically, as shown in FIGS. 67 and 68, grating filters 601 and 602 arranged in the optical axis direction
And a photoelectric conversion element 603, a scanning position detector 604 disposed near the grating filter 601, and these components 60.
It is composed of a case 605 accommodating 1 to 604 and a piezoelectric actuator 606. Lattice filters 601, 6
Numeral 02 has striped spatial gratings A and B, respectively. The spatial grating A is parallel to the main scanning direction b of the laser beam L, and the spatial grating B is inclined by a small angle.

[0139] Here, by making the pitch dimension d ₂ of the pitch dimension d ₁ and a spatial lattice B space lattice A mutually, the light receiving surface 603a, to control the number of moiré fringes projected on 603b it can. In the seventh embodiment, d
By setting ₁ ≠ d ₂ , one bright portion of the moire fringe is projected on the beam detector 600. The photoelectric conversion element 603 is a two-divided sensor having light receiving surfaces 603a and 603b, and each of the light receiving surfaces 603a and 603b outputs a current proportional to the amount of received light. Light receiving surfaces 603a, 6
The division line 03b is substantially parallel to the sub-scanning direction c.

The laser beam L transmitted through the two grating filters 601 and 602 forms moire fringes 35 on the light receiving surfaces 603a and 603b. The inclination of the moire fringes 35 changes due to defocus. That is, the bright portion of the moire fringe 35 in the front focus state is rotated clockwise and inclined rightward (see FIG. 69), and the bright portion of the moire fringe 35 in the focused state is orthogonal to the main scanning direction b (FIG. 70). The bright portion of the moire fringe 35 in the back focus state is rotated left and inclined leftward (see FIG. 71).

From the two light receiving surfaces 603a and 603b, respective output currents I _a and I _b are obtained in proportion to the amount of incident light. These output currents I _a, I _b is transferred to the AF control unit 521, after being converted respectively voltage value V _a, the V _b, the values of the V _a and V _b is treated with a difference circuit, ( V _a
Deriving the value of −V _b ). The focusing position of the laser beam is determined based on the result. That is, if (V _a −V _b ) is 0, it is determined that the camera is in focus (see FIG. 70), if negative, it is determined that the camera is in front focus (see FIG. 69). It is determined (see FIG. 71).

From the determination result, the moving direction of the cylindrical lens 503 is determined, and a control signal is transmitted to the stepping motor 518. The stepping motor 518 rotates in either the forward or reverse direction, and rotates the cylindrical lens 50.
3 is moved by a predetermined amount on the optical axis. When the lens 503 moves away from the laser diode 501, the focus is adjusted backward, and when the lens 503 moves closer, the focus is adjusted forward. The amount of one movement of the lens 503 is set to a predetermined value at which the focal point moves by about 0.01 mm.
In order for such movement to reach a focused state, that is, (V _a
Repeat until −V _b ) becomes 0.

Further, the procedure for adjusting the focusing position of the laser beam will be described in detail with reference to the electric circuit diagram of the autofocus control section 521 shown in FIG. 2-split optical sensor 60
The output from each of the light receiving surfaces 603a and 603b is photoelectrically converted and output as a current corresponding to the amount of incident light. Thus, each of the light receiving surface 603a, the light portion of the Moire fringes 35 is projected to 603b, the output current I _a from the light receiving surface 603a is I-V - is converted into a voltage by the (current-voltage) conversion circuit 705, a voltage output as v _a, it is inputted to the amplifier circuit 709. Amplifier circuit 709, and V _a amplifies the voltage output v _a,
The signal is output to the peak hold circuit 715.

Similarly, output current I from light receiving surface 603b is
_b is I-V - is converted into a voltage by the (current-voltage) conversion circuit 707, a voltage output v _b, is inputted to the amplifier circuit 711. Amplifier circuit 711, a V _b amplifies the voltage output v _b, and outputs to the peak hold circuit 716. Peak hold circuit 715 holds the peak of the input voltage V _a, the output is V (A) to the difference circuit 717. Further, the peak hold circuit 716 holds the peak of the input voltage _Vb , and outputs the output V (B) to the difference circuit 717. Difference circuit 7
17 is a difference V (C) (V) between the input V (A) and V (B).
(C) = V (A) −V (B)) to the window comparator circuit 718 and the comparator circuit 719.
The difference circuit 717 is provided on the light receiving surface 60 of the two-divided optical sensor 603.
The difference between the amount of light incident on 3a and the amount of light incident on 603b is detected, and the shape of the moire fringes can be known from the difference as described above.

Further, as a digital judgment, the window comparator circuit 718 and the comparator circuit 71
9 is used. The window comparator circuit 718 determines that the output V (C) of the difference circuit 717 is equal to the reference voltages V _{ref1 to} V _ref2.
Is within the range, it is determined that the moire fringes are vertical stripes, and it is determined that the focus is in focus, and the motor ON signal is made inactive.
If it is outside the reference voltages V _{ref1 to} V _ref2 , it is determined that focusing is not performed, and the motor ON signal is activated. This motor ON signal is output to the motor control circuit 721. The comparator circuit 719 _supplies the reference voltage V _ref3 (mainly V _ref1
And V _ref2 ) to determine whether the shape of the moiré stripe is rotating clockwise or counterclockwise.
The signal is output as a high-level or low-level signal. This is used as a motor forward / reverse rotation signal, and the motor control circuit 7
21.

The motor control circuit 721 drives the stepping motor 518 based on the motor ON signal and the motor forward / reverse rotation signal, moves the cylindrical lens 503 in the front-back direction on the optical axis, and moves the photosensitive drum 53 of the laser beam.
Adjust the focusing position on 0. The motor ON signal is also transmitted as a signal q to the printer main body control unit 524, and A
A gate is set using the ND element 720, and whether or not to perform autofocus control is controlled by ON / OFF of an autofocus release switch 526 (see FIG. 67) provided in the printer main body control unit 524.

Further, the auto focus control section 521
In order to synchronize the position of the laser beam spot with respect to the photosensitive drum 530, a beam detection photodiode 512 is disposed upstream of the laser scanning. And
The beam detection signal from the photodiode 512 is sent to the printer main body control unit 524 via the beam detection circuit 523. Based on this beam detection signal, a laser beam is emitted from a beam detector 60 located outside the image printing area.
The laser diode 501 is made to emit light so that it is also incident on zero.

Next, the scanning position detector 604 will be described. When the optical path of the laser beam L shifts in the sub-scanning direction,
Moiré fringes projected on the light receiving surfaces 603a and 603b move in the main scanning direction, causing erroneous detection. For this purpose, the optical unit may be made of a metal material such as aluminum which is resistant to thermal deformation. However, there is a problem that the manufacturing cost is increased.

Therefore, the first beam detector 600 is provided with the scanning position detector 604, and always has the laser beam L, the grating filters 601 and 602, and the photoelectric conversion element 60.
3 so that the positional relationship of the scanning position detector 60 becomes constant.
A mechanism is provided for moving the grating filters 601 and 602 and the photoelectric conversion element 603 up and down in the sub-scanning direction in accordance with the output signal of No. 4.

The scanning position detector 604 has a light receiving surface 604
The light receiving surfaces 604a and 604b output a current proportional to the amount of received light. These output currents I _a, I _b is transferred to the AF control unit 521, the voltage value V _a, respectively, V _b
After being converted into the values of the V _b of V _a is treated with the differential circuit to calculate the value of (V _a -V _b).

Usually, in the initial state, as shown in FIG. 73, the division lines of the light receiving surfaces 604a and 604b are set so as to be aligned with the center of the spot Lb of the laser beam L. In this case, the light receiving surface 604a, because the amount of light incident on the 604b are equal, the light receiving surface 604a, the output current I _a value equal from 604b, I _b can be obtained. Therefore, (V _a −
The value of V _b ) becomes zero. However, when the optical path of the laser beam is shifted upward in the sub-scanning direction as shown in FIG. 74 due to a change in environment, (V _a −V _b ) becomes positive. Conversely, as shown in FIG. 75, when the optical path of the laser beam is shifted downward in the sub-scanning direction, (V _a −V _b )
Becomes negative. Therefore, based on this result, (V
_a −V _b ) so that the value of the piezoelectric actuator 6 becomes zero.
06 to move the beam detector 600 up and down in the sub-scanning direction so that the laser beam L and the lattice filter
The positional relationship between the photoelectric conversion element 602 and the photoelectric conversion element 603 is kept constant.

The procedure for adjusting the scanning position of the laser beam will be described in detail with reference to the electric circuit diagram of the scanning position detector control unit shown in FIG. Outputs from the light receiving surfaces 604a and 604b of the two-divided optical sensor 604 are photoelectrically converted and output as a current corresponding to the amount of incident light. Thus, each of the light receiving surface 604a, the laser beam L is irradiated to 604b, the output current I _a from the light receiving surface 604a is I-V - is converted into a voltage by the (current-voltage) conversion circuit 735, a voltage output v _a , To the amplifier circuit 737. Amplifier circuit 737, and V _a amplifies the voltage output v _a, and outputs to the peak hold circuit 739.

Similarly, output current I from light receiving surface 604b is
_b is I-V - is converted into a voltage by the (current-voltage) conversion circuit 736, a voltage output v _b, is inputted to the amplifier circuit 738. Amplifier circuit 738, a V _b amplifies the voltage output v _b, and outputs to the peak hold circuit 740. The peak hold circuits 739 and 740 respectively provide input voltages V _a and V _b
Is held, and output as output signals s and t to an input port of a microcomputer (not shown) in the printer main body control unit 524. The microcomputer calculates the difference (V _a −V _b ), and if it determines that there is an optical path shift based on the result, outputs a piezoelectric actuator drive signal u to the piezoelectric actuator drive power supply 529 and the piezoelectric actuator 606. To move the beam detector 600 up and down in the sub-scanning direction.

Further, the procedure of focus state detection and focus adjustment will be described with reference to the flowcharts shown in FIGS. 77 and 78. FIG. 77 is a main flowchart showing a control procedure of the printer main body control unit 524. When the power of the printer is turned on, the initialization of the control program is performed in step S101, and the autofocus control (described later) is performed in step S102. Next, step S
At 103, serial data is received from an image controller (not shown). For example, in a printer, an image signal and a timing signal are input. Further, step S10
In step S4, it is checked whether a print request has been made. If the print request has been made, the laser diode 501 blinks based on the image signal in step S105, and print processing is performed. Next, in step S106, normal processing such as checking of various necessary flags is performed regardless of whether printing is in progress or in standby. In step S107, the status of the printer main body control unit 524 is transmitted to the image controller as serial data. And step S
At 108, the count-up of the routine timer is checked, and if it has, the process returns to step S103.

FIG. 78 is a flow chart showing the procedure of the auto focus control. In step S109, the polygon motor 505 is driven, and in step S110, the laser diode 501 is turned on. Next, in step S111, the optical path shift is measured. As a result, if it is determined in step S112 that there is an optical path shift, the drive voltage of the drive power supply 529 of the piezoelectric actuator 606 is set in step S113, and again, Step S11
Returning to step 1, the optical path deviation measurement is repeated.

If it is determined in step S112 that there is no optical path shift, the focus state is detected in step S114.
In step S115, it is determined whether or not the subject is in focus. If it is determined in step S115 that the subject is in focus, the process directly proceeds to the next step S119. If it is determined in step S115 that the subject is not in focus,
In step S116, it is determined whether the camera is in the front focus state. If the camera is in the front focus state, in step S117, the stepping motor 518 is rotated forward to rotate the cylindrical lens 503.
Is moved away from the laser diode 501 to adjust the focus backward. If it is determined in step S116 that the camera is not in the front focus state (that is, the camera is in the rear focus state), in step S118, the stepping motor 518 is determined.
Is reversed, and the cylindrical lens 503 is moved in a direction approaching the laser diode 501 to adjust the focus forward.

After adjusting the focal position, step S1 is performed.
Returning to 14, the focus state is detected, and it is determined in step S115 whether or not the object is in focus. If it is in focus, the process proceeds to the next step S119.
The processing from step S116 is continued again. Again, the focus state is detected in step S115, and if the focus state is reached, the stepping motor 518 is immediately stopped in step S119. Then, in step S120, the polygon motor 505 is turned off, and in step S121,
After the light emission of the laser diode 501 is stopped, FIG.
It returns to the main flowchart shown in FIG.

As described above, according to the seventh embodiment, immediately after the power is turned on to the apparatus, even if the optical path shifts, the in-focus state is detected stably, and the focus adjustment is performed. Therefore, the laser beam scanning optical device can always be used in an appropriate state. Although the above-described apparatus moves the entire beam detector 600, the present invention is not limited to this. For example, only the photoelectric conversion element 603 may be moved by a piezoelectric actuator or the like. In this case, when the optical path of the laser beam is shifted upward in the sub-scanning direction (see FIG. 74), the photoelectric conversion element 603 is moved to the left in FIG. 68 in parallel with the main scanning direction b. Conversely, when the optical path is shifted downward in the sub-scanning direction (see FIG. 75), the photoelectric conversion element 603 is moved parallel to the main scanning direction b in FIG.
To the right.

Alternatively, only the grating filter 602 may be moved by a piezoelectric actuator or the like. In this case, when the optical path is shifted upward in the sub-scanning direction (see FIG. 74), the grating filter 602 is moved to the right in FIG. 68 in parallel with the main scanning direction b. Conversely, when the optical path is shifted downward in the sub-scanning direction (see FIG. 75), the grating filter 602 is moved to the left in FIG. 68 in parallel with the main scanning direction b.

(Second Beam Detector) The beam detector is not limited to the above-described one, but may be the second beam detector shown in FIGS. In addition,
Unlike the first beam detector 600, the second beam detector does not include a mechanism for vertically moving the grating filter and the photoelectric conversion element in the sub-scanning direction.

As shown in FIG. 79, the beam detector includes a photoelectric conversion element 610.
Divided light receiving surfaces 610a, 610b, 610c, 61
0d, and each light receiving surface 6
10a to 610d output a current proportional to the amount of received light. One set of light receiving surfaces 610a and 610b, light receiving surface 610c
And 610d constitute another set. And
The light receiving surfaces 610a and 610b are designed to be line symmetric with respect to the line 611, and the light receiving surfaces 610c and 610d are designed to be line symmetric with respect to the line 611. Further, when the optical axis of the laser beam is shifted, the position where the moiré fringes 35 projected on the light receiving surfaces 610a to 610d are shifted in the main scanning direction, so that the light receiving surfaces 610a and 610b or 610c are shifted.
The photoelectric conversion element 610 is arranged such that the line 611 serving as a reference for line symmetry of the line 610d and the line 610d substantially coincides with each other in the main scanning direction.

The laser beam L transmitted through the two grating filters 601 and 602 forms one bright portion of the moiré fringes 35 over the light receiving surfaces 610a to 610d. Moiré stripe 3
5 changes the inclination by defocus. That is,
The bright portion of the moiré fringe 35 in the front focus state rotates rightward and tilts rightward (see FIG. 80), and the bright portion of the moiré fringe 35 in the focused state is orthogonal to the main scanning direction b (see FIG. 81). The bright portion of the moire fringe 35 in the back focus state is rotated left and inclined leftward (see FIG. 82).

Then, the four light receiving surfaces 610a to 610d
From the output currents I _a ,
I _b, I _c, I _d is obtained. These output current I _a ~I _d
After it is transferred to the AF control unit 521, respectively converted into a voltage value _{V a, V b, V c} , to V _d, (V _a +
_Vc ) and the value of ( _Vb + _Vd ) are processed by a difference circuit,
(V _a + V _c) - to derive a value of (V _b + V _d). The focusing position of the laser beam is determined based on the result. _{That, (V a + V c)} - (V b + V d) is determined to focus state if 0 (see FIG. 81), before it is positive is determined that the focus state (see FIG. 80), a negative If so, it is determined that the camera is in the back focus state (see FIG. 82). This relationship does not change even if the optical path shift of the laser beam in the sub-scanning direction occurs and the moiré fringes are shifted in the main scanning direction.

The procedure for adjusting the focusing position of the laser beam will be described in detail with reference to the electric circuit diagram of the autofocus control section 521 shown in FIG. 4-split optical sensor 61
The outputs from the light receiving surfaces 610a to 610d of 0 are photoelectrically converted and output as a current corresponding to the amount of incident light. Accordingly, when the bright portion of the Moire fringes 35 on the light receiving surface 610a~610d is projected, the output current I _a from the light receiving surface 610a is I-V - is converted into a voltage by the (current-voltage) conversion circuit 750, a voltage output as v _a, it is inputted to the amplifier circuit 754. The amplification circuit 754 amplifies the voltage output v _a to obtain V _a ,
Output to the addition circuit 758.

Similarly, output current I from light receiving surface 610c is
_c is I-V - is converted into a voltage by the (current-voltage) conversion circuit 751, a voltage output v _c, is input to the amplifier circuit 755. Amplifier circuit 755, and V _c to amplify the voltage output v _c, and outputs to the adder circuit 758. Adding circuit 758 adds a voltage output V _a and V _c, and outputs to the peak hold circuit 760.

Similarly, output current I from light receiving surface 610b is
_b is I-V - is converted into a voltage by the (current-voltage) conversion circuit 752, a voltage output v _b, is inputted to the amplifier circuit 756. Amplifier circuit 756, a V _b amplifies the voltage output v _b, and outputs to the adder circuit 759. Output current I _d from the light-receiving surface 610d is I-V - is converted into a voltage by the (current-voltage) conversion circuit 753, a voltage output v _d, the amplifier circuit 7
52 is input. Amplifier circuit 757, and V _d amplifies a voltage output v _d, and outputs to the adder circuit 759. Adding circuit 759 adds the voltage output V _b and V _d, and outputs to the peak hold circuit 761.

The peak hold circuit 760 detects the input voltage V
_a + V _c is held and the output V
(A). The peak hold circuit 761 holds the peak of the input voltage V _b + V _d, the difference circuit 762 outputs V (B). The difference circuit 762 calculates the difference V (C) between the input V (A) and V (B) (V (C) = V (A) −V
(B)) is output to the window comparator circuit 763 and the comparator circuit 764. The difference circuit 762 includes four
The difference between the amount of light incident on the light receiving surfaces 610a and 610c of the split sensor 610 and the amount of light incident on the light receiving surfaces 610b and 610d is detected, and the shape of the moire fringe can be known from the difference.

Further, as a digital judgment, a window comparator circuit 763 and a comparator circuit 763 are provided.
4 is used. The window comparator circuit 763 sets the output V (C) of the difference circuit 762 to the reference voltages V _{ref1 to} V _ref2.
Is within the range, it is determined that the moire fringes are vertical stripes, and it is determined that the focus is in focus, and the motor ON signal is made inactive.
If it is outside the reference voltages V _{ref1 to} V _ref2 , it is determined that focusing is not performed, and the motor ON signal is activated. This motor ON signal is output to the motor control circuit 766. The comparator circuit 764 _supplies the reference voltage V _ref3 (mainly V _ref1
And V _ref2 ) to determine whether the shape of the moiré stripe is rotating clockwise or counterclockwise.
The signal is output as a high-level or low-level signal. This is used as a motor forward / reverse rotation signal, and the motor control circuit 7
66 is output.

The motor control circuit 766 drives the stepping motor 518 based on the motor ON signal and the motor forward / reverse rotation signal, moves the cylindrical lens 513 in the front-back direction on the optical axis, and moves the laser beam to the photosensitive drum 530.
Adjust the focusing position above. The motor ON signal is also transmitted as a signal q to the printer main body control section 524, and the signal ON from the
A gate is applied using the D element 765, and whether or not to perform autofocus control is controlled by turning on and off an autofocus release switch 526 (see FIG. 67) provided in the printer main body control unit 524.

As described above, since the shape of the light receiving surfaces 610a to 610d of the photoelectric conversion element 610 is designed to be triangular, even if the optical path shift of the laser beam in the sub-scanning direction occurs, the moire fringes are generated in the main scanning direction. Even if it is shifted, the inclination of the moire fringes can be detected. As a result, it is possible to stably and accurately detect the direction and amount of the shift of the condensing position in the sub-scanning direction on the surface to be scanned.

The shape of the light receiving surface of the photoelectric conversion element 610 does not need to be limited to a triangle, and may have trapezoidal light receiving surfaces 615a, 615b, 615c, and 615d as shown in FIG. The light receiving surfaces 615a and 615
b constitutes one set, and the light receiving surfaces 615c and 615d constitute another set. And the light receiving surfaces 615a and 615b.
It is designed to be line-symmetric with respect to a line 616 parallel to the main scanning direction, and the light receiving surfaces 615c and 615d are
It is designed to be line symmetric with respect to.

The photoelectric conversion element 610 is not limited to a four-divided optical sensor. For example, the light-receiving surfaces 610a and 610
b divided sensor or light receiving surface 610
The optical sensor may be a two-division optical sensor combining c and 610d, or may be a three-division optical sensor, or an optical sensor with five or more divisions. The striped spatial grating A of the grating filter 601 may be parallel to the main scanning direction of the laser beam as described above, or may be parallel to the sub-scanning direction.

[Eighth Embodiment, FIGS. 85 and 86] The first to seventh embodiments have been described by taking as an example an apparatus in which the beam detector is arranged behind the focus position of the laser beam L. However, in the eighth embodiment, a case will be described in which the beam detector is disposed ahead of the focus position of the laser beam L. As shown in FIGS. 85 and 86, the beam detector is installed outside the image area near the optically substantially equivalent position to the surface to be scanned, and the grating filters 621 and 622 and the photoelectric conversion element arranged in the optical axis direction. 625. The grating filters 621 and 622 have striped spatial gratings A and B, respectively. The spatial grating A is parallel to the main scanning direction b of the laser beam L, and the spatial grating B is inclined by a small angle. The focus position Z1 of the laser beam L is located behind the beam detector.

The laser beam L of the convergent light transmitted through the two grating filters 621 and 622 forms moire fringes on the light receiving surfaces 625a and 625b of the photoelectric conversion element 625. This moiré fringe can be displayed by a linear equation similar to the linear equation (1) of the first embodiment. Therefore, the inclination of the moire fringes in the focused state can be calculated using the above-described relational expression (4).

[0175]

(Equation 6)

Is obtained. As shown in FIG. 86, the focus position Z
When 1 moves to Z2 with a shift of Δl (see the laser beam L ′ indicated by the dotted line in FIG. 86), the front focus state is established, and the inclination of the moire fringe at that time is

[0177]

(Equation 7)

Is obtained. The tilt of the moire fringes in the back focus state is

[0179]

(Equation 8)

Is obtained. From (14), (15) and (16), it can be seen that the inclination of the moire fringes changes due to the defocus. That is, the moire fringes in the front focus state rotate left and tilt to the left, and the moire fringes in the back focus state rotate right and tilt to the right. This laser beam scanning optical apparatus can project the laser beam L onto the light receiving surfaces 625a and 625b in the form of converged light without using a reduction optical system, and the size of the moire fringes is reduced by the light receiving surfaces 625a and 625b.
It can be made to have substantially the same size as. As a result, the number of bright portions and dark portions of moire fringes formed on the light receiving surfaces 625a and 625b increases, and erroneous detection hardly occurs.

Further, a detailed description will be given using numerical values.
The pitch dimension d ₁ of the spatial grid A of the grid filter 621 is set to 1
20 μm, the pitch dimension d ₂ of the spatial grating B of the grating filter 622 is 60 μm, and the minute inclination angle α of the spatial grating B is 4
Degree, distance l from focus position Z1 to grating filter 621
₁ 80 mm, 40 mm distance l ₂ from the focus position Z1 to the grating filter 622, and the distance l ₃ from the focus position Z1 to the photoelectric conversion element 625 was 30 mm, the inclination of the Moire fringes 35 are the first embodiment From the relational expression (5) of the condition,
The following values are obtained:

[Cosα-｛(l ₁ d ₂ ) / (l
₂ d ₁ )｝] / sin α = −0.035 Therefore, tan φ = −0.035, and φ = −2
[Degree]. Thereby, the inclination of the moiré fringes 35 becomes −
88 [degrees]. On the other hand, the pitch dimension P of the moire fringes 35
Since f = l ₃ d ₁ / l ₁ , the following numerical values are obtained from the relational expression (6) of the first embodiment.

P = (f / sin α) × cos (φ−α)
= 0.64 [mm] Here, when a two-segment photodiode having a width of 3 mm and a height of 1 mm is used as the photoelectric conversion element 625, the light and dark portions of about four moire fringes 35 are photoelectrically converted. Light can be received by the element 625. Thus, the light receiving surface 6
A plurality of moiré fringes 35 are projected on 25a and 625b,
As in the first embodiment, the light receiving surfaces 625a, 625b
By detecting the phase difference ΔT between the peak values of the respective output waveforms, the change in the inclination of the moiré fringes 35 can be known.

As described above, since the focused laser beam L is projected onto the photoelectric conversion element 625, the reduction optical system (for example, the cylindrical lenses 103 and 104 of the first embodiment) used in the above embodiment is omitted. The size of the device can be reduced. [Ninth Embodiment, FIGS. 87 and 88] In order to improve the detection accuracy of the defocus, it is preferable to increase the inclination angle of the moire fringes with respect to the defocus amount. However, if the focus position is located outside the area between the two grating filters of the beam detector as in the first to eighth embodiments, the image is projected onto the light receiving surface when defocused. Since the respective pitch dimensions of the two spatial gratings are enlarged (or reduced), the amount of change in the tilt angle of the moire fringes is small, and high detection accuracy cannot be obtained.

In order to solve this problem, in the ninth embodiment, the focus position of the laser beam is arranged between the two grating filters of the beam detector. As shown in FIG. 87 and FIG. 88, the beam detector is installed outside the image area near an optically substantially equivalent position to the surface to be scanned, and has grating filters 621 and 622 and a cylindrical lens 623 arranged in the optical axis direction. , 624 and a photoelectric conversion element 625. The focus position Z1 of the laser beam L is located between the grating filters 621 and 622.

A cylindrical lens 6 forming a reduction optical system
23 and 624, the cylindrical lens 623 has a light condensing function only in the main scanning direction b, and the cylindrical lens 6
24 has a light condensing function only in the sub-scanning direction c. Therefore, the laser beam L transmitted through the two grating filters 621 and 622 is condensed by the cylindrical lenses 623 and 624 and then received by the light receiving surfaces 625 a and 625 of the photoelectric conversion element 625.
Moire fringes are formed on 25b.

This moiré fringe can be displayed by the same linear equation as the linear equation (1) of the first embodiment. Therefore, the inclination of the moire fringes in the focused state can be calculated using the above-described relational expression (4).

[0188]

(Equation 9)

Is obtained. f = l ₃ d ₁ / l ₁ , g = l ₃ d ₂ /
because it is l _2, as shown in FIG. 88, (see laser beam L indicated by a dotted line in FIG. 88 ') when the focus position Z1 is moved in the Z2 displaced .DELTA.l, a state before the focus, f
_{= (L 3 + Δl) d} 1 / (l 1 -Δl), g = (l 3 + Δ
1) Since d ₂ / (l ₂ + Δl), the inclination of the moire fringe at that time is

[0190]

(Equation 10)

Is obtained. The tilt of the moire fringes in the back focus state is

[0192]

[Equation 11]

Is obtained. From (17), (18), and (19), it can be seen that the inclination of the moire fringes changes due to the defocus. Since this beam detector has the focus position Z1 disposed between the two grating filters 621 and 622, the size can be reduced. In addition, the inclination angle of the moire fringes with respect to the defocus amount increases, and the accuracy of detecting the defocus can be improved.

Further description will be made specifically using numerical values.
The pitch dimensions d ₁ and d ₂ of the spatial gratings A and B are each set to 125
μm (although the pitch dimensions of A and B need not always be equal, accuracy is further improved by making the pitch dimensions equal).
Distance l ₁ from focus position Z1 to spatial grid A is 20 m
m, the distance l ₂ from the focus position Z1 to the spatial grid B is 20
In the case of mm, the inclination of the moire fringes in the initial state was set so that φ = −3.5 [degrees] from the relational expression (16). Next, the focus position is set to Δl
= 0.2 mm, φ = 5.8 [degrees] from the relational expression (18). Therefore, -3.5-5.
8 = -9.3 [degrees].

On the other hand, for comparison, the change amount of the inclination angle of the moiré fringes with respect to the defocus amount is calculated for an apparatus in which the beam detector is disposed behind the focus position of the laser beam as in the first embodiment. did. The pitch dimension d ₁ of the spatial grid A is 125 μm, the pitch dimension d ₂ of the spatial grid B is 250 μm, the small inclination angle α of the spatial grid B is 7 degrees, the distance l ₁ from the focus position Z1 to the spatial grid A is 40 mm, If the focus position Z1 and the distance l ₂ to spatial grating B and 80 mm, setting the inclination of the moire fringes in the initial state, so that phi = -3.5 [degrees] from the equation (5) did.
Next, assuming that the focus position is shifted by Δl = 0.2 mm, φ = −2.3 [degree] is obtained from the relational expression (7). Therefore, the amount of change in the inclination angle of the moire fringes with respect to the defocus amount is -3.5-(-2.3) =-1.2 [degrees]. This value is smaller than the case where the focus position of the laser beam is arranged between the two grating filters 621 and 622.
Extremely small.

[Tenth Embodiment, FIGS. 89 to 97] When detecting a change in the rotation of moiré fringes due to defocusing, the holder holding the grid filter is subject to thermal expansion and heat due to environmental changes (particularly temperature changes). When contracted, the distance from the in-focus position to the grating filter fluctuates, and there is a concern that the rotational change of the moiré fringe may be erroneously detected.

Therefore, the tenth embodiment will explain a laser beam scanning optical device having a structure in which the inclination of the moire fringes does not easily change with changes in the environment (temperature). (In the case where the beam detector is disposed behind the focus position of the laser beam L) As shown in FIG. 89, the beam detector 630 includes grating filters 631, 632 and photoelectric conversion elements arranged in the optical axis direction. 633, and a holder 641 for holding these components 631 to 633. The beam detector 630 is disposed behind the focus position Z1 of the laser beam L. The holder 641 has a lattice filter 63
1, a through hole 641a is provided. On the other hand, a screw hole 645a is provided in the body frame 645 of the laser beam scanning optical device near the focus position Z1. The beam detector 630 is fixed to the main body frame 645 by screwing a screw 642 inserted through the through hole 641a into the screw hole 645a. That is, the beam detector 630 is disposed near the main frame 6 near the grating filter 631.
45.

The laser beam L transmitted through the two grating filters 631 and 632 forms moire fringes on the light receiving surface of the photoelectric conversion element 623. This moiré fringe can be displayed by a linear expression similar to the linear expression (1) of the first embodiment. The pitch dimension d ₁ of the spatial grid A of the grid filter 631 is 125 μm, the pitch dimension d ₂ of the spatial grid B of the grid filter 632 is 250 μm, the small inclination angle α of the spatial grid B is 4 degrees, and the grid filter starts from the in-focus position Z1. 631
The distance l ₁ to 40 mm, when the distance l ₂ from the focus position Z1 to grating filter 632 and 80 mm, the inclination of the Moire fringes in the initial state, the relational expression of the first embodiment (5), below It becomes the numerical value of.

[0199]

(Equation 12)

If the temperature rises by 25 degrees,
The holder 641 is made of aluminum (linear expansion coefficient: 2.3 × 1)
When made from 0 ^-5), the inclination of the Moire fringes,

[0201]

(Equation 13)

The following is obtained. For comparison, temporarily use the holder 641.
Is provided near the lattice filter 632 and the beam detector 630 is fixed to the main body frame 645 near the lattice filter 632. When the temperature rises by 25 degrees, the slope of the moire fringes becomes

[0203]

[Equation 14]

The amount of change is represented by the beam detector 63
0 is larger than the case where 0 is fixed to the main body frame 645 in the vicinity of the lattice filter 631. In addition, if the through holes 641a of the holder 641 are temporarily replaced with the lattice filters 631 and 632,
, And the beam detector 630 is connected to the grating filter 63.
Consider a case where the camera is fixed to the main body frame 645 at an intermediate position between 1 and 632. When the temperature rises by 25 degrees, the slope of the moire fringes becomes

[0205]

(Equation 15)

[0206] The amount of change is represented by the beam detector 63.
0 is larger than the case where 0 is fixed to the main body frame 645 in the vicinity of the lattice filter 631. As described above, by adopting the structure in which the beam detector 630 is fixed to the main body frame 645 in the vicinity of the grating filter 631, the variation in the inclination of the moire fringes with respect to the temperature change can be reduced, and the focus state can be reduced. A scanning optical device with high detection accuracy can be obtained.

Note that there are various other methods for fixing the beam detector 630 to the main frame 645 near the grating filter 631. For example, as shown in FIG. 90, an adhesive 646 may be applied to the holder 641 in the vicinity of the lattice filter 631 and fixed to the main body frame 645. Also,
As shown in FIG.
The other end of the holder 641 fixed to the main frame 5 is fixed to the main body frame 645 by an elastic member 647 with screws 648.
And the internal stress due to thermal expansion and thermal contraction
The holder 641 may be more firmly fixed to the main body frame 645 without causing the holder 64 to be generated.

(When the Beam Detector is Arranged Forward of the Focused Position of the Laser Beam L) As shown in FIG. 92, the beam detector 649 includes grating filters 631 and 632 arranged in the optical axis direction. Photoelectric conversion element 633 and holder 650 for holding these components 631 to 633
It is composed of The beam detector 649 is disposed ahead of the focus position Z1 of the laser beam L. The holder 650 has a through hole 650 a near the lattice filter 632.
Is provided. On the other hand, a screw hole 645a is provided in the body frame 645 of the laser beam scanning optical device near the focus position Z1. The beam detector 649 inserts the screw 651 inserted through the through hole 650a into the screw hole 645a.
To the main body frame 645. That is, the beam detector 649 is fixed to the main body frame 645 near the grating filter 632.

The laser beam L transmitted through the two grating filters 631 and 632 forms moire fringes on the light receiving surface of the photoelectric conversion element 633. This moiré fringe can be displayed by a linear expression similar to the linear expression (1) of the first embodiment. The pitch dimension d ₁ of the spatial grid A of the grid filter 631 is 120 μm, the pitch dimension d ₂ of the spatial grid B of the grid filter 632 is 60 μm, the small inclination angle α of the spatial grid B is 4 degrees, and the grid filter starts from the in-focus position Z1. When the distance l ₁ to the column 631 is 80 mm, and the distance l ₂ from the focus position Z1 to the lattice filter 632 is 40 mm, the inclination of the moire fringes in the initial state can be obtained from the relational expression (5) of the first embodiment. The following numerical values are obtained.

[0210]

(Equation 16)

When the temperature rises by 25 degrees,
The holder 650 is made of aluminum (linear expansion coefficient: 2.3 × 1)
When made from 0 ^-5), the inclination of the Moire fringes,

[0212]

[Equation 17]

The following is obtained. For comparison, tentatively, holder 650
It is assumed that the screw through hole 650 a is provided near the lattice filter 631 and the beam detector 649 is fixed to the main body frame 645 near the lattice filter 631. 25 temperature
As the temperature rises, the slope of the moiré stripes becomes

[0214]

(Equation 18)

The amount of the change is equal to the beam detector 64
9 is larger than the case where it is fixed to the main body frame 645 in the vicinity of the lattice filter 632. In addition, if the through holes 650a of the holder 650 are temporarily inserted into the lattice filters 631 and 632,
, And the beam detector 649 is connected to the grating filter 63.
Consider a case where the camera is fixed to the main body frame 645 at an intermediate position between 1 and 632. When the temperature rises by 25 degrees, the slope of the moire fringes becomes

[0216]

[Equation 19]

[0217] The amount of change is represented by the beam detector 64.
9 is larger than the case where it is fixed to the main body frame 645 in the vicinity of the lattice filter 632. As described above, by adopting the structure in which the beam detector 649 is fixed to the main body frame 645 in the vicinity of the grating filter 632, the variation in the inclination of the moire fringes with respect to the temperature change can be reduced, and the focus state can be reduced. A scanning optical device with high detection accuracy can be provided.

Note that there are various other methods for fixing the beam detector 649 to the main frame 645 near the grating filter 632. For example, as shown in FIG. 93, an adhesive 655 may be applied so as to cover a through hole 650a provided in the holder 650 near the lattice filter 632 and fixed to the main body frame 645. As shown in FIG. 94, the other end of the holder 650 fixed to the main body frame 645 with the screw 651 is attached to the main body frame 645 with the screw 6.
The holder 650 is more firmly pressed by the elastic member 657 fixed at 58 without generating internal stress due to thermal expansion or thermal contraction in the holder 650.
45 may be fixed.

(Grating Filters 631 and 63 of Beam Detector)
As shown in FIG. 95, the beam detector 660 includes grating filters 631 and 632 and a photoelectric conversion element 633 arranged in the optical axis direction. A holder 661 for holding these components 631 to 633 is configured. The beam detector 660 is arranged so that the focus position Z1 of the laser beam L is located between the grating filters 631 and 632. The holder 661 is provided with a through hole 661a between the lattice filters 631 and 632. On the other hand, a screw hole 645a is provided in the body frame 645 of the laser beam scanning optical device near the focus position Z1. The beam detector 660 includes a screw 66 inserted into the through hole 661a.
2 is fixed to the main body frame 645 by screwing it into the screw hole 645a. That is, the beam detector 660 is fixed to the main body frame 645 at a position between the grating filters 631 and 632.

The laser beam L transmitted through the two grating filters 631 and 632 forms moire fringes on the light receiving surface of the photoelectric conversion element 633. This moiré fringe can be displayed by a linear expression similar to the linear expression (1) of the first embodiment. The pitch dimension d ₁ of the spatial grid A of the grid filter 631 is 125 μm, the pitch dimension d ₂ of the spatial grid B of the grid filter 632 is 125 μm, the small inclination angle α of the spatial grid B is 4 degrees, and the grid filter starts from the in-focus position Z1. 631
When the distance l ₁ from the focus position Z1 to the lattice filter 632 is 40 mm, and the distance l ₂ from the focus position Z1 to the lattice filter 632 is 40 mm, the inclination of the moire fringes in the initial state is as follows from the relational expression (5) of the first embodiment. It becomes the numerical value of.

[0221]

(Equation 20)

When the temperature rises by 25 degrees,
The holder 661 is made of aluminum (linear expansion coefficient: 2.3 × 1)
When made from 0 ^-5), the inclination of the Moire fringes,

[0223]

(Equation 21)

Is the same as the initial state. For comparison, it is assumed that the through hole 661a of the holder 661 is provided near the lattice filter 631, and the beam detector 660 is fixed to the main body frame 645 near the lattice filter 631. When the temperature rises by 25 degrees, the slope of the moire fringes becomes

[0225]

(Equation 22)

Then, the state changes from the initial state. Also, temporarily,
A through hole 661a of the holder 661 is provided near the grating filter 632, and the beam detector 660 is connected to the grating filter 632.
Consider a case where it is fixed to the main body frame 645 in the vicinity. When the temperature rises by 25 degrees, the slope of the moire fringes becomes

[0227]

(Equation 23)

Then, the state changes from the initial state. As described above, the beam detector 660 is connected to the grating filters 631 and 632.
By adopting a structure that is fixed to the main body frame 645 at a position between, the variation in the inclination of the moiré fringes with respect to the temperature change can be reduced, and a scanning optical device with high detection accuracy of a focused state is provided. be able to. In particular, at a position intermediate between the grating filters 631 and 632, the beam detector 66
When 0 is fixed to the main body frame 645, the amount of dimensional change between the lattice filters 631 and 632 due to a temperature change can be offset so as not to affect the inclination of the moire fringes.

Note that there are various other methods for fixing the beam detector 660 to the main frame 645 at a position between the grating filters 631 and 632. For example, as shown in FIG. 96, an adhesive 665 may be applied so as to cover the through hole 661a provided between the lattice filters 631 and 632 of the holder 661, and fixed to the main body frame 645. Further, as shown in FIG. 97, the other end of the holder 661 fixed to the main body frame 645 with the screw 662 is pressed by the elastic member 667 fixed to the main body frame 645 with the screw 668, and the thermal expansion is performed. The holder 661 may be more firmly fixed to the frame main body 645 without causing the holder 661 to generate internal stress due to heat or thermal shrinkage.

[Eleventh Embodiment, FIGS. 98 to 101] As described in the first embodiment, in the case of a beam detector that generates moire fringes using two grating filters, each of the grating filters Since the inclination of the moiré fringes also changes due to the pitch error of the spatial gratings A and B, there is a risk of erroneous detection. Therefore, in the first embodiment, this problem is avoided by regulating the pitch error Δd ₂ of the spatial grating B. Further, since the beam detector is installed outside the image area near the optically substantially equivalent position to the surface to be scanned, the space is limited. However, in the case of a beam detector provided with two grating filters, it is necessary to arrange the two grating filters at a fixed distance, which limits the size reduction.

Therefore, in the eleventh embodiment, a laser beam scanning optical device provided with a beam detector using only one grating filter to solve the above problem will be described. The laser beam scanning optical device according to the eleventh embodiment includes:
Since it has the same structure as that of the device of the first embodiment except for the beam detector 700, detailed description thereof is omitted.

As shown in FIG. 98, the beam detector 700
Is composed of a half mirror 701, a grating filter 702, a mirror 703, and a photoelectric conversion element 704 that are arranged outside the image area near an optically substantially equivalent position with respect to the surface to be scanned and arranged in the optical axis direction. The grating filter 702 has a striped spatial grating A, and this spatial grating A
Is parallel to the main scanning direction b. Photoelectric conversion element 70
Reference numeral 4 denotes a two-divided sensor having light receiving surfaces 704a and 704b, and each of the light receiving surfaces 704a and 704b outputs a current proportional to the amount of light. The mirror 703 is arranged at a slight angle with respect to the main scanning direction b.

Next, the beam detector 7 having the above configuration is described.
The operation and effect of 00 will be described with reference to FIG.
The laser beam L incident on the half mirror 701 transmits half of the light amount and reaches the grating filter 702. The remaining half amount of light is reflected by the half mirror 701 and then enters, for example, the SOS optical sensor 17 to generate a vertical synchronization signal for determining a print start position for each scanning line.
A part of the laser beam L that has reached the grating filter 702 is blocked by the spatial grating A when passing through the filter 702, and becomes a striped pattern 710 parallel to the scanning direction b as shown in FIG. I do.

[0234] The mirror 703 uses the laser beam L as the optical axis.
By rotating (skew) by a small angle with respect to FIG.
A stripe pattern inclined at a small angle with respect to the scanning direction b as shown in FIG.
Pattern 711 is reflected. Laser beam reflected
L passes through the grating filter 702 again,
Generates alley fringes. The light transmitted through the lattice filter 702
The half of the light amount of the laser beam L is reflected by the half mirror 701.
The light is condensed and collected, and the light receiving surface 704 of the photoelectric conversion element 704
Moire fringes are formed on a and 704b.

The moiré fringes can be displayed by the same linear equation as the linear equation (1) of the first embodiment.
Here, α is the striped pattern 7 before reflection by the mirror 703.
10 is a minute tilt angle of the striped pattern 711 after reflection with respect to 10. l ₁ is a focusing position Z1 located on the downstream side along the optical path from the grating filter 702 located on the upstream side of the optical axis.
, L ₂ is the focus position Z located on the upstream side of the optical axis.
1 and a grating filter 70 located downstream along the optical path
The distance l ₃ to the photoelectric conversion element 7 located on the downstream side along the optical path from the focusing position Z1 located on the upstream side of the optical axis.
04. Therefore, the inclination of the moire fringes in the focused state can be calculated using the above-described relational expression (4).

[0236]

(Equation 24)

Is obtained. Here, since d ₁ = d ₂ , the change in the inclination of the moire fringes is determined by the change in the distance from the focus position to the spatial grid A. That is, f = l ₃ d ₁ / l ₁ ,
Since g = l ₃ d ₂ / l ₂ , as shown in FIG. 99, when the focus position Z1 shifts by Δl to Z2 (see the laser beam L ′ indicated by a dotted line in FIG. 99), the front focus is adjusted. F = (l ₃ + Δl) d ₁ / (l ₁ −Δl), g
= (L ₃ + Δl) d ₂ / (l ₂ + Δl), d ₁ = d ₂ ,

[0238]

(Equation 25)

Is obtained. The tilt of the moire fringes in the back focus state is

[0240]

(Equation 26)

Is obtained. From (20), (21) and (22), it can be seen that the inclination of the moire fringes changes due to the defocus. As described above, this beam detector 700
Can generate moiré fringes with one grating filter 702, so that the change in the inclination of moiré fringes caused by a pitch error between two spatial gratings caused by a beam detector using two grating filters is eliminated. be able to. Moreover,
Since there is only one lattice filter, miniaturization can be easily achieved.

[Twelfth Embodiment, FIGS. 102 and 10
3] In the case of a beam detector having two grating filters,
Since it is necessary to arrange two grating filters at a fixed distance, there is a limit to miniaturization. However, since the beam detector is installed outside the image area near the optically substantially equivalent position to the surface to be scanned, the space is limited and the arrangement may be difficult.

Therefore, in the twelfth embodiment, in order to solve the above problem, a description will be given of a laser beam scanning optical device provided with a beam detector that does not use a grating filter.
The laser beam scanning optical device according to the twelfth embodiment has the same structure as the device according to the first embodiment except for the beam detector 720, and a detailed description thereof will be omitted. As shown in FIG. 102, the beam detector 720 is installed outside the image area near an optically substantially equivalent position to the surface to be scanned,
It comprises folding mirrors 721 and 722 arranged in the optical axis direction and a photoelectric conversion element 723. A stripe-shaped space grating A is formed on the left side of the reflection surface of the return mirror 721, and the space grating A is parallel to the main scanning direction b of the laser beam L. Similarly, on the left side of the reflection surface of the reflecting mirror 722, a striped spatial grid B is formed, and the spatial grid B is inclined at a small angle with respect to the main scanning direction b. The photoelectric conversion element 723 is a two-divided sensor having two light receiving surfaces, and each light receiving surface outputs a current proportional to the amount of light.

Next, the beam detector 7 having the above configuration is described.
20 will be described. A part of the laser beam L incident on the return mirror 721 at the portion where the spatial grating A is formed is blocked by the spatial grating A, is reflected in a stripe pattern parallel to the scanning direction b, and is reflected. The reflected laser beam L is incident on the turning mirror 722 in the portion where the spatial grating B is formed. The folding mirror 722 further blocks a part of the laser beam L with a spatial grating B, and at this time, generates moire fringes in the laser beam. The laser beam L reflected by the folding mirror 722 forms Moire fringes on the light receiving surface of the photoelectric conversion element 723. This moiré fringe can be displayed by a linear expression similar to the linear expression (1) of the first embodiment,
The tilt of the moire fringes changes due to the defocus.

On the other hand, the laser beam L incident on the turning mirror 721 in the portion where the spatial grating A is not formed is
Folding mirror 7 at the portion where spatial grating B is not formed
The light enters the optical sensor 17 for SOS via the SOS 22 and generates a vertical synchronization signal for determining a print start position for each scan. As described above, this beam detector 720 forms spatial gratings A and B on the folding mirrors 721 and 722 for the SOS optical sensor without using a grating filter, and uses these folding mirrors 721 and 722 as grating filters. , The arrangement becomes easy and the number of parts can be reduced.

There are various other types of beam detectors that do not use a grating filter. For example, as shown in FIG. 103, a beam detector 740 including a folding mirror 741, a window 742, and a photoelectric conversion element 743 arranged in the optical axis direction may be used. Folding mirror 7
41, a striped space grating A is formed on the left side of the reflection surface,
This spatial grating A is parallel to the main scanning direction b of the laser beam L. Similarly, a striped spatial grid B is formed on the left side of the surface of the window 742, and the spatial grid B is inclined by a small angle with respect to the main scanning direction b. Window 7
For 42, a transparent glass plate, a transparent film, or the like is used. The photoelectric conversion element 743 includes two light receiving surfaces 743a and 743a.
The light receiving surface 743a, 743b outputs a current proportional to the amount of light.

The laser beam L incident on the mirror 741 at the portion where the spatial grating A is formed is reflected by the mirror 741 and then passes through the window 742 at the portion where the spatial grating B is formed. Moire fringes are formed on the light receiving surface of the conversion element 743. On the other hand, the return mirror 741 in the portion where the spatial grating A is not formed
Is incident on the SOS optical sensor 17 through the window 742 where the spatial grating B is not formed. However, after the laser beam L first enters the window 742 and passes therethrough, the turning mirror 7
Needless to say, a configuration such as 41 may be adopted. [Other Embodiments] The laser beam scanning optical device according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the gist.

The type and arrangement of the optical elements such as the fθ lens are arbitrary. Also, of the two filters having the striped spatial grid, the filter disposed on the light source side does not necessarily have to be parallel to the main scanning direction or parallel to the sub-scanning direction. The filters arranged may be parallel to the main scanning direction or parallel to the sub-scanning direction.
However, in this case, the amount of light received by the photoelectric conversion element is slightly reduced.

[0249]

FIG. 104 shows a laser beam scanning optical device manufactured by the present inventors. The same components and portions as those in FIG. 1 of the first embodiment are denoted by the same reference numerals. Motor 9
For No. 3, a linear step actuator whose motor shaft moves linearly when driven is used. By directly moving the lens holder 92 connected to the motor shaft by the motor shaft, the focusing lens 3 attached to the lens holder 92 can move back and forth on the optical axis. The focusing position on the body drum 30 is adjusted. Incidentally, reference numeral 91 denotes a housing.

Further, as a result of an experiment performed under the following conditions, the ability to detect defocus is high, and the focus adjustment can be performed in an extremely short time. That is, the photoelectric conversion element 105: a two-division sensor, the minute inclination angle α of the spatial grid B: 4 degrees, the pitch dimension d ₁ of the spatial grid A: 125 μm, the pitch dimension d ₂ of the spatial grid B: 250 μm, from the focus position to the spatial grid A. Distance l ₁ : about 40 mm Distance l from the focus position to the spatial grid B l ₂ : about 80 mm Lens drive distance of one pulse of the motor: 25 μm Focus position change amount when temperature changes by 25 degrees: about 1.
5 mm Lens moving amount: Focusing position moving amount = 2: 1 If the temperature changes by 5 degrees between pages under the above conditions, as shown in FIG. 105, the motor 93 is turned off until the focusing operation is completed. It was confirmed that about 20 pulses were driven. The time obtained by adding the motor driving time to the sensing and signal processing time, that is, the autofocus processing time was about 70 milliseconds. Generally, a copying speed of 30
Since the non-printing time between pages of a digital copying machine or a printer is about 500 milliseconds, it is possible to cope with even higher-speed machines.

[0251]

As is apparent from the above description, according to the present invention, the moiré fringe generating means for modulating the laser beam emitted from the laser light source to generate a moiré fringe pattern is provided in optical communication with the surface to be scanned. Since it is arranged near the substantially equivalent position, the direction and amount of the shift of the condensing position on the surface to be scanned can be determined, the detection capability is extremely high, and the focus adjustment can be performed in a short time.

Further, the light receiving element is a photoelectric conversion element having a plurality of light receiving surfaces and outputting an electric signal corresponding to the laser beam incident on each of the light receiving surfaces. By providing the phase difference detecting means for detecting the phase difference of the electric signal, it is possible to easily determine the change in the inclination of the moire fringes. In addition, by disposing a reduction optical system between the first and second filters and the photoelectric conversion element, moiré fringes can be reduced and defocus can be stably detected.

[Brief description of the drawings]

FIG. 1 shows a first example of a laser beam scanning optical device according to the present invention.
The perspective view showing an embodiment.

FIG. 2 is an exploded perspective view of the beam detector shown in FIG.

FIG. 3 is an exploded perspective view showing a comparative example of the beam detector shown in FIG. 2;

FIG. 4 is an explanatory diagram of the comparative example shown in FIG.

FIG. 5 is an explanatory diagram for guiding the inclination of moiré fringes formed on the surface to be scanned of the beam detector shown in FIG. 2;

FIG. 6 is a side view showing a positional relationship between a focused position of a laser beam and a beam detector.

FIG. 7 is an explanatory diagram showing a relationship between a spot diameter of a laser beam and an interval between moiré fringes.

FIG. 8 is a graph showing an output waveform of the beam detector in the case shown in FIG. 7;

FIG. 9 is an explanatory diagram showing the relationship between the spot diameter of a laser beam and the interval between moiré fringes.

FIG. 10 is a graph showing an output waveform of the beam detector in the case shown in FIG. 9;

11 is a graph showing a specific output waveform of the beam detector shown in FIG.

FIG. 12 is an explanatory diagram showing a relationship between moiré fringes in a focused state and a light receiving surface of a photoelectric conversion element.

FIG. 13 is an explanatory diagram showing a relationship between moire fringes in a front focus state and a light receiving surface of a photoelectric conversion element.

FIG. 14 is an explanatory diagram showing a relationship between a moire fringe in a back focus state and a light receiving surface of a photoelectric conversion element.

FIG. 15 is an electric circuit diagram showing a control circuit block diagram of the beam detector shown in FIG. 2;

FIG. 16 is an explanatory diagram showing a positional relationship between a spot of a laser beam and a light receiving surface of a photoelectric conversion element.

Figure 17 is a graph position of the spot indicates the output waveform of the beam detector in the case of Lb _1.

FIG. 18 is a graph showing the output waveform of the beam detector when the position of the spot is Lb ₂ .

FIG. 19 is a graph showing the output waveform of the beam detector when the position of the spot is Lb ₃ .

FIG. 20 is an exploded perspective view showing a modification of the first moiré fringe selecting means.

FIG. 21 is an exploded perspective view showing another modification of the first moiré fringe selecting means.

FIG. 22 is a timing chart of the control circuit block shown in FIG.

FIG. 23 is a front view showing a light receiving surface of a beam detector in which moire fringes are inclined in an initial state.

24 is a graph showing an output waveform of the beam detector shown in FIG.

FIG. 25 is a front view showing the variation in the inclination of the moire fringes.

FIG. 26 is a graph showing an output waveform of the beam detector shown in FIG. 25.

FIG. 27 is an electric circuit diagram showing a delay circuit.

FIG. 28 is a perspective view showing a moving unit for moving the photoelectric conversion element in the direction of rotation of the moire fringes.

FIG. 29 is a front view of the moving unit shown in FIG. 28.

FIG. 30 is an exploded perspective view of the beam detector showing a state in which the photoelectric conversion element is moved in the tilt rotation direction of the moire fringes by the moving unit shown in FIG. 28;

FIG. 31 is an explanatory diagram showing a relationship between moiré fringes in a focused state and a light receiving surface of a photoelectric conversion element.

FIG. 32 is an explanatory diagram showing a relationship between moire fringes in a front focus state and a light receiving surface of a photoelectric conversion element.

FIG. 33 is an explanatory diagram showing a relationship between a moire fringe in a back focus state and a light receiving surface of a photoelectric conversion element.

FIG. 34 is an electric circuit diagram showing a control circuit block diagram of the beam detector shown in FIG. 2;

FIG. 35 is a timing chart of the control circuit block shown in FIG. 34;

FIG. 36 is an exploded perspective view of a beam detector showing a modification of the photoelectric conversion element.

FIG. 37 is an exploded perspective view of a beam detector showing another modification of the photoelectric conversion element.

FIG. 38 is an exploded perspective view of a beam detector showing still another modified example of the photoelectric conversion element.

FIG. 39 is an exploded perspective view of a beam detector showing a modification of the reduction optical system.

FIG. 40 is an exploded perspective view of a beam detector showing a second embodiment of the laser beam scanning optical device according to the present invention.

FIG. 41 is an explanatory diagram showing a positional relationship between a spot of a laser beam and a light receiving surface of a photoelectric conversion element.

Figure 42 is a graph position of the spot indicates the output waveform of the beam detector in the case of Lb _1.

FIG. 43 is a graph showing an output waveform of the beam detector when the position of the spot is Lb ₂ .

FIG. 44 is a graph showing an output waveform of the beam detector when the position of the spot is Lb ₃ .

FIG. 45 is an electric circuit diagram showing a control circuit block diagram of the beam detector shown in FIG. 40;

FIG. 46 is an exploded perspective view of a beam detector showing a modification of the photoelectric conversion element.

FIG. 47 is an exploded perspective view of a beam detector showing another modification of the photoelectric conversion element.

FIG. 48 is an exploded perspective view of a beam detector showing a third embodiment of the laser beam scanning optical device according to the present invention.

49 is an electric circuit diagram showing a control circuit block diagram of the beam detector shown in FIG. 48.

FIG. 50 is a timing chart of the control circuit block shown in FIG. 49;

FIG. 51 is an exploded perspective view of a beam detector showing a fourth embodiment of the laser beam scanning optical device according to the present invention.

FIG. 52 is an explanatory diagram showing pitch intervals of moiré fringes in a focused state.

FIG. 53 is an explanatory diagram showing pitch intervals of moiré fringes in a front focus state.

54 is an electric circuit diagram showing a control circuit block diagram of the beam detector shown in FIG. 51.

FIG. 55 is a graph showing the signal output of the beam detector.

FIG. 56 is an exploded perspective view of a beam detector showing a modification of the photoelectric conversion element.

FIG. 57 is an exploded perspective view of a beam detector showing another modified example of the photoelectric conversion element.

FIG. 58 is an exploded perspective view of a beam detector showing a fifth embodiment of the laser beam scanning optical device according to the present invention.

FIG. 59 is an explanatory diagram showing a relationship between moiré fringes in a focused state and a light receiving surface of a photoelectric conversion element.

FIG. 60 is an explanatory diagram showing a relationship between moire fringes in a front focus state and a light receiving surface of a photoelectric conversion element.

FIG. 61 is an explanatory diagram showing a relationship between a moire fringe in a back focus state and a light receiving surface of a photoelectric conversion element.

FIG. 62 is an exploded perspective view of a beam detector used in a sixth embodiment of the laser beam scanning optical device according to the present invention.

FIG. 63 is an exploded perspective view of a beam detector showing a modification of the photoelectric conversion element.

FIG. 64 is a graph showing an output waveform of the beam detector shown in FIG. 63.

FIG. 65 is a perspective view showing a modification of the beam detector.

FIG. 66 is a perspective view showing another modification of the beam detector.

FIG. 67 is a perspective view showing a seventh embodiment of the laser beam scanning optical device according to the present invention.

FIG. 68 is a perspective view of the beam detector shown in FIG. 67.

FIG. 69 is an explanatory diagram showing a relationship between moire fringes in a front focus state and a light receiving surface of a photoelectric conversion element.

FIG. 70 is an explanatory diagram showing a relationship between moiré fringes in a focused state and a light receiving surface of a photoelectric conversion element.

FIG. 71 is an explanatory diagram showing the relationship between moiré fringes in the back focus state and the light receiving surface of the photoelectric conversion element.

FIG. 72 is an electric circuit diagram showing a block diagram of an autofocus control circuit.

FIG. 73 is an explanatory diagram showing a positional relationship between a spot of a laser beam and a light receiving surface of a photoelectric conversion element.

FIG. 74 is another explanatory diagram showing the positional relationship between the spot of the laser beam and the light receiving surface of the photoelectric conversion element.

FIG. 75 is still another explanatory diagram showing the positional relationship between the spot of the laser beam and the light receiving surface of the photoelectric conversion element.

FIG. 76 is an electric circuit diagram showing a scanning position detector control circuit block diagram.

FIG. 77 is a flowchart showing a control procedure of a printer main body control unit.

FIG. 78 is a flowchart showing an autofocus control procedure.

FIG. 79 is an exploded perspective view showing a second beam detector.

FIG. 80 is an explanatory view showing the relationship between the moire fringes in the front focus state and the output waveform of the beam detector.

FIG. 81 is an explanatory view showing the relationship between moire fringes in a focused state and the output waveform of a beam detector.

FIG. 82 is an explanatory view showing the relationship between the moire fringes in the back focus state and the output waveform of the beam detector.

FIG. 83 is an electric circuit diagram showing a block diagram of an autofocus control circuit.

FIG. 84 is a front view showing a modification of the photoelectric conversion element.

FIG. 85 is an exploded perspective view of a beam detector used in an eighth embodiment of the laser beam scanning optical device according to the present invention.

FIG. 86 is a side view showing the positional relationship between the focused position of the laser beam and the beam detector.

FIG. 87 is an exploded perspective view of a beam detector used in a ninth embodiment of the laser beam scanning optical device according to the present invention.

FIG. 88 is a side view showing the positional relationship between the focused position of the laser beam and the beam detector.

FIG. 89 is a sectional view showing a mounting structure of a beam detector used in a tenth embodiment of the laser beam scanning optical device according to the present invention.

FIG. 90 is a sectional view showing a modification of the mounting structure shown in FIG. 89;

FIG. 91 is a sectional view showing another modification of the attachment structure shown in FIG. 89;

FIG. 92 is a cross-sectional view showing a mounting structure of the beam detector in a case where the focusing position of the laser beam and the positional relationship of the beam detector are different from those in FIG. 89;

FIG. 93 is a sectional view showing a modification of the mounting structure shown in FIG. 92;

FIG. 94 is a sectional view showing another modification of the attachment structure shown in FIG. 92;

FIG. 95 is a cross-sectional view showing a mounting structure of the beam detector in a case where the focusing position of the laser beam and the position of the beam detector are different from those in FIG. 89;

FIG. 96 is a sectional view showing a modification of the mounting structure shown in FIG. 95;

FIG. 97 is a sectional view showing another modification of the attachment structure shown in FIG. 95;

FIG. 98 is an exploded perspective view of a beam detector used in an eleventh embodiment of the laser beam scanning optical device according to the present invention.

FIG. 99 is a side view showing the positional relationship between the focused position of the laser beam and the beam detector.

FIG. 100 is a plan view showing a stripe pattern of a laser beam before mirror reflection.

FIG. 101 is a plan view showing a stripe pattern of a laser beam after mirror reflection.

FIG. 102 is an exploded perspective view of a beam detector used in a twelfth embodiment of the laser beam scanning optical device according to the present invention.

103 is an exploded perspective view showing a modification of the beam detector shown in FIG. 102.

FIG. 104 is a plan view showing a specific embodiment of the laser beam scanning optical device according to the present invention.

FIG. 105 is an explanatory diagram showing an autofocus processing time.

[Explanation of symbols]

1, 501 laser diode 3, 503 focusing lens 6, 504 polygon mirror 7, 507 fθ lens 24 signal processing circuit 25 control circuit 26 focusing lens drive control unit 30, 530 photosensitive drum 100, 150 , 160, 180, 600, 630, 6
49,660 ... Beam detectors 101,131,141,151,161,171,1
81, 621, 631... Lattice filter (first filter) 102, 132, 142, 152, 162, 172, 1
82, 622, 632 ... Lattice filter (second filter) 105, 116a to 116f, 118a to 118d, 1
20, 121, 135, 155, 165, 167, 16
8,173,183,184,186,603,62
5,633: photoelectric conversion elements 105a, 105b, 120a to 120c, 121a to
121d, 155a, 155b, 173a to 173d,
183a, 184a, 184b, 603a, 603b,
625a, 625b ... light receiving surface 103, 104, 133, 134, 143, 153, 1
54, 163, 164, 623, 624 ... cylindrical lens 117 ... positive lens 204, 213, 217 ... comparator 205, 214, 218 ... flip-flop 206, 209, 215 ... AND element 220 ... microcomputer 219 ... programmable timer 521 ... AF Controller 700, 720, 740 Beam detector 701 Half mirror 702 Grid filter 703 Mirror 704, 723, 743 Photoelectric conversion element 704a, 704b, 743a, 743b Light receiving surface 721, 722, 741 Folding mirror 742 ... Window A, B ... Spatial grid

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuo Kanai 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Inventor Kenji Takeshita Azuchi-cho, Chuo-ku, Osaka-shi, Osaka 2-3-13 Osaka International Building Minolta Co., Ltd. (72) Inventor Keiji Oe 2-3-1-13 Azuchicho, Chuo-ku, Osaka City, Osaka Prefecture Osaka International Building Minolta Co., Ltd. (72) Inventor Yasushi Nagasaka Osaka Osaka International Building Minolta Co., Ltd. 2-3-13 Azuchicho, Chuo-ku, Osaka-shi

Claims (6)

[Claims] 1. A laser beam scanning optical system which focuses a laser beam emitted from a laser light source via a deflector and an optical element to a minute point and scans a surface to be scanned in a line at a substantially constant speed. In the apparatus, adjusting means for adjusting the condensing position of the laser beam emitted from the laser light source, and arranged near an optically equivalent position to the surface to be scanned and modulating the laser beam emitted from the laser light source A moiré fringe generating means for generating a moiré fringe pattern; a light receiving element for receiving the moiré fringe pattern generated by the moiré fringe generating means; and Control means for correcting the laser beam condensing position described above; and a laser beam scanning optical device. 2. The moiré fringe generating means is, in order from the side of the laser light source, a first filter having a striped spatial grid, and is inclined by a small angle with respect to the direction of the spatial grid of the first filter. 2. The laser beam scanning optical device according to claim 1, wherein a second filter having a striped spatial grating is arranged. 3. The laser beam scanning optical device according to claim 2, wherein the striped spatial grating of the first filter is parallel to the main scanning direction of the laser beam. 4. The apparatus according to claim 1, further comprising a second control unit for causing the laser light source to emit light at a fixed point, wherein the striped spatial grating of the first filter is parallel to a sub-scanning direction of the laser beam. The laser beam scanning optical device according to claim 2. 5. The light receiving element has a plurality of light receiving surfaces,
A photoelectric conversion element for outputting an electric signal corresponding to the laser beam incident on each of the light receiving surfaces, and having a phase difference detecting means for detecting a phase difference between the electric signals output from the photoelectric conversion element; The laser beam scanning optical device according to claim 1, wherein: 6. The laser beam scanning optical device according to claim 1, wherein a reduction optical system is provided between said moiré fringe generating means and said light receiving element.